SI-2066 Plug a soundness hole higher order type params, overriding

PolyType-s parameterized by higher order type parameters (HOTPs)
should only be relatable with <:< or =:= if the variances of their
type parameters line up. This is only enforced for HOTPs defined in
method type arguments.

Invariant type parameters subsume variant ones. Concretely, as
described by @S11001001:

> A method taking [F[_]] can implement a method taking [F[+_]].
> Likewise, a method taking [F[_[+_]]] can implement a method
> taking [F[_[_]]], as with [F[_[_[_]]]] implementing [F[_[_[+_]]]],
> and so on, the variance subsumption flipping at each step.
>
> This is just the opposite of the variance for passing type
> parameters to either instantiate types or call methods; a F[+_]
> is a suitable F[_]-argument, a F[_[_]] a suitable F[_[+_]]-argument,
> and so on.
>
> All of the above rules can be duplicated for contravariant positions
> by substituting - for +. Also, something similar happens for
> weakening/strengthening bounds, I believe.

These cases are tested in the `// okay` lines in `neg/t2066.scala`.
SI-8027 REPL double tab regression

Where did double tab go?  "The shadow knows."

The regression was introduced by the last flurry
before we were left to wallow in whatever white
space remained.

Some xs put other xs under erasure.

It's clear that somebody's daughter walked into
the room and asked for a story, because, shockingly,
the case arrows don't line up.

We need a plug-in for Jenkins, or I guess Travis, to
fail the build if arrows and equals don't align,
because it clearly indicates a lapse of some kind.
SI-8010 Fix regression in erasure double definition checks

Calls to `Symbol#info` during scope iteration considered harmful.

Looks like calling `info` during this Scope iteration is triggering
the ExplicitOuter info transformer, which "makes all super accessors
and modules in traits non-private, mangling their names.". This name
change necessitates a rehashing of the owning scope, which I suspect
is enough to corrupt the ScopeEntry-s being traversed in
`checkNoDeclaredDoubleDefs`.

The upshot was that we encountered the same symbol twice, which was
reported as being a double-definition.

This problem only showed up after 086702d8a74, which did nothing
worse then change the order in which `{e, e1}.sym.info` were
forced.

I inspected SymbolPairs/OverridingPairs which *appear* to be immune
as they only test flags during scope iteration; infos are not used
until later, at which point we're iterating a temporary scope that
isn't part of the type of the owner of the symbols.
Merge pull request #3209 from dotta/SI-7982-on-2.10.x

 make askLoadedType unload arguments out of the PC by default,
SI-7995 completion imported vars and vals

Imported member vals and vars were always marked inaccessible, even
if referencing them at the location of the completion is valid in code.
The accessible flag is now set accordingly to the accessibility of the getter.
SI-8029 Avoid multi-run cyclic error with companions, package object

The bug report suggests this problem only became visible in the
IDE *after* 2.10.3, but I tested an IDE with exactly 2.10.3 and
saw the same problem.

In fact, my test case fails as far back as 2.10.0. I suspect the
problem showed up after 816cecf9a9, which checks that pairs of
companion symbols are codefined eagerly in Namers.

This commit modifies the check of `rawInfo ne NoType`
in `isCoDefinedWith` to avoid triggering adaptation of types from
the previous run. I'm not sure of the precise intent of that check.
I looked at c9861cd198 (genesis of isCoDefinedWith). Before that we
get back to 3761cb4b3a1 (the dawn of Subversion.)
[nomaster] better error messages for various macro definition errors

backport of 1d3ec4e708154ec05554f540d7d68ed55dc12426
SI-4841 Plugins get a class path

Let -Xplugin specify a class path (or multiple of them).

Each entry can be a jar or dir, and the first entry to supply
a plugin descriptor defines the plugin to load.

If no plugin is found on the path, then issue a warning if `-Xdev`.
This honors the legacy silent treatment (which scala-ide tests for).

In the proposed scheme, each plugin gets a class loader so that
plugins are isolated from each other.

Presumably, if compiler plugins were a rich ecosystem, in which
shared dependencies were required in incompatible versions, this
would have become a requirement by now.

(Updated with a `DirectTest` that uses two plugins, but keeping
the following as documentation.)

Partest can't do multiple plugins yet, but this is what it looks like:

```
skalac -Xplugin:sample.jar:useful.jar:util,needful.jar:another.jar:util,needful.jar:util:exploded -Xplugin-require:sample,another,other foo.scala

skalac -Xplugin:sample.jar:useful.jar:util,needful.jar:another.jar:util,needful.jar:util:exploded -Xplugin-require:sample,other -Xplugin-disable:another foo.scala

skalac -Xplugin:sample.jar:useful.jar:util,sample.jar:useful.jar:util -Xplugin-require:sample foo.scala
```
The manual test shows three plugins with various permutations of jars and dirs.

The manual test demonstrates that plugins only see classes on their class path:

```
Initializing test.plugins.SamplePlugin
needful.Needful? Failure(java.lang.ClassNotFoundException: needful.Needful)
useful.Useful? Success(class useful.Useful)
Initializing more.plugins.AnotherPlugin
needful.Needful? Success(class needful.Needful)
useful.Useful? Failure(java.lang.ClassNotFoundException: useful.Useful)
Initializing other.plugins.OtherPlugin
```

Disabling a plugin results in a message instead of silent suppression:

```
Disabling plugin another
```

The duplicate plugin class test must still be honored:

```
Ignoring duplicate plugin sample (test.plugins.SamplePlugin)
Initializing test.plugins.SamplePlugin
needful.Needful? Failure(java.lang.ClassNotFoundException: needful.Needful)
useful.Useful? Success(class useful.Useful)
```

If the path is bad, then missing classes will report which plugin induced
the error:

```
Error: class not found: util/Probe required by test.plugins.SamplePlugin
Error: class not found: util/Probe required by more.plugins.AnotherPlugin
Initializing other.plugins.OtherPlugin
needful.Needful? Success(class needful.Needful)
useful.Useful? Failure(java.lang.ClassNotFoundException: useful.Useful)
error: Missing required plugin: sample
error: Missing required plugin: another
two errors found
```
Merge pull request #3232 from xeno-by/topic/macro-error-messages-210x

[nomaster] better error messages for various macro definition errors
[backport] SI-7439 Avoid NPE in `isMonomorphicType` with stub symbols.

`originalInfo` can return null for stub symbols; deal with that
as we used to before a regression in 016bc3db.

After this change, we can once again delete A_1.class and still compile
code instantiating B_1. (A_1 is only referred to in a method signature
of B_1 which is not called from our code.)

	scala> new B_1
	warning: Class A_1 not found - continuing with a stub.
	res0: B_1 = B_1@5284b8f9

In practice, this situation arises when someone uses a third
party class that was compiled against other libraries not avaialable
on the current compilation classpath.

(cherry picked from commit a95432168204964e4f6c4571e781559c1640f2d8)
Merge pull request #3223 from retronym/ticket/8010-2.10.x

SI-8010 Fix regression in erasure double definition checks
Merge pull request #3230 from retronym/backport/7439

[backport] SI-7439 Avoid NPE in `isMonomorphicType` with stub symbols.
SI-8050 [Avian] Skip instrumented tests

Instrumentation is (currently) not supported on Avian.
This causes
- tests instrumented/InstrumentationTest.scala and
- instrumented/inline-in-constructors
to fail.

Let's skip these tests on Avian.
SI-8052 Disallow `macro` as an identifier

Note that the change could look a lot cleaner, at the cost of returning
more generic error messages. I decided that at least for 2.11 I'll keep
scalac remembering that macro was a standard identifier name once, so
that we can point out more precisely what's wrong with users' code.
SI-8054 Fix regression in TypeRef rebind with val overriding object

Regressed in 80767383fd / SI-7928

The condition added in that commit are necessary after refchecks but
poisonous before.

This still seems rather fragile: I wonder if `eliminateModuleDefs`
in `RefChecks` ought to flag the module symbol as `ARTIFACT` after
creating the accessor, so as to signal that it shouldn't be bound
anymore?
Merge pull request #3229 from retronym/ticket/8029

SI-8029 Avoid multi-run cyclic error with companions, package object
SI-8046 Fix baseTypeSeq in presence of type aliases
Pending test for SI-6161

Not solved with base type dealiasing
SI-7618 Remove octal number literals

This also fixes a spurious detection of octal literals in floating
point literals: Literals like 01.23 are neither deprecated nor planned
for removal.
SI-8019 Make Publisher check PartialFunction is defined for Event

Reactions are PartialFunctions, so if events come through
indiscriminately that the listener is not defined for, errors occur. Eg:

--
Exception in thread "AWT-EventQueue-0" scala.MatchError: FocusGained(scala.swing wrapper scala.swing.TextField
--

A Coursera thread with people affected by this issue:

https://class.coursera.org/reactive-001/forum/thread?thread_id=1315