Refactor DirectTest so java can be tested.

There was no way to make a java compilation unit.
Now there is.
SI-7398 Add support for java8 default methods

In classfile parser: mark symbols which represent interface
methods yet have code attributes with new flag DEFAULTMETHOD.
These must be kept distinct from regular method bodies so that
an error can be issued when a regular concrete method is
overridden without the override keyword, but not when the
overridden method is a default.

In java source parser: mark Modifiers of interface default
methods with DEFAULTMETHOD flag.

Writing the test was everything I dreamed, and more! However,

  % test/partest --debug test/files/run/t7398.scala
  Skipping java8-specific test under java version 1.7.0_21
  testing: [...]/files/run/t7398.scala                                  [  OK  ]
  All of 1 tests were successful (elapsed time: 00:00:04)

  % test/partest --debug test/files/run/t7398.scala
  Attempting java8-specific test under java version 1.8.0-ea
  testing: [...]/files/run/t7398.scala                                  [  OK  ]
  All of 1 tests were successful (elapsed time: 00:00:13)
SI-7426 Crash in pickler.

I wonder if the supply of copy-pasted code, and the bugs
which always accompany it, will ever run low. Here we have
a couple hundred lines of tree traversal which appears
roughly identical in structure to a different couple hundred
lines of tree traversal, except one calls methods called
putXXX and the other calls methods called writeXXX.

Except there was one call to writeXXX among all the putXXX
calls. Guess where it was crashing.

This entire file should be expunged.
SI-7271 fixes positions of string interpolation parts

Positions of static parts are now set explicitly during parsing rather
than filled in wholesale during subsequent atPos after parsing.

I also had to change the offsets that scanner uses for initial static
parts of string interpolations so that they no longer point to the
opening double quote, but rather to the actual beginning of the part.
SI-5634 eliminate overly verbose error message

In fact I couldn't see where the error message described in
the ticket is being produced, and I'm supposing it has
already vacated the premises. I went through ClassfileParser
and UnPickler, the two enclaves most likely to harbor the
spewer, and hardened the output. No printlns, tighter
assertion messages, and string interpolation for aesthetics.
We're not savages.
SI-7441 Don't ramble on about inapplicable implicits.
SI-5734 Allow setting of socket timeout for remote actors

TcpService is locked while connections are being established, preventing
messages being sent to remote nodes. There was no way to specify a connect
timeout, so the service was waiting for a ConnectException to be thrown if
the remote node was unavailable (which can take several minutes).

Added a system property to allow setting a socket connect timeout to
prevent the TcpService from being locked for minutes at a time.

Default behaviour is unchanged, all tests pass and the patch has been
running in production without issue.
SI-7325 cleans up corner cases of percent handling in StringContext.f

See comments in code for the exhaustive list of the cases handled.
Also note that treatment of non-formatting percents has been changed.
Embedding literal %'s now requires escaping.

Moreover, this commit also features exact error positions for string
interpolation, something that has been impossible until the fix for
SI-7271, also included in this patch.
literal() now assigns a position to the tree it produces

At all its callsites except for a single one, the results of literal()
were wrapped in atPos(in.offset), so the simplification was pretty much
warranted. Thanks @paulp
Scaladoc: fixing small typo in PartialFunction.scala

Fixing a one-letter typo in the documentation of PartialFunction.scala (from "an plain" to "a plain").
fixes a crash in ReflectionUtils.systemProperties

Due to SI-7465 we were erroneously assuming that System.getProperties
only contains string key and string values. This led to a CCE when there
was something else.
removes the traces of always on debug diagnostics

pun intended
replaces inferBootClasspath with a simple lookup at sun.boot.class.path

It's not like we're achieving any generality by iterating through all
keys in System.getProperties and looking for ones which resemble
"boot.class.path", so let's be simpler.
Merge pull request #2488 from paulp/issue/7441

SI-7441 Don't ramble on about inapplicable implicits.
Merge pull request #2473 from paulp/pr/2.10.2/5634

SI-5634 eliminate overly verbose error message
Merge pull request #2458 from paulp/issue/7426-210

SI-7426 Crash in pickler.
Merge pull request #2461 from scalamacros/ticket/7325

Some fixes for string interpolation
pull request feedback
Merge pull request #2456 from paulp/pr/jdk8-210x

SI-7398 Add support for java8 default methods
Merge pull request #2481 from martinmcnulty/socket-timeout

SI-5734 Allow setting of socket timeout for remote actors