SI-7779 Account for class name compactification in reflection

We have to assume that the classes we are reflecting on were
compiled with the default value for -Xmax-classfile-name (255).

With this assumption, we can apply the same name compactification
as done in the regular compiler.

The REPL is particularly prone to generating long class names
with the '$iw' prefixes, so this is an important fix for runtime
reflection.

Also adds support for getting the runtime class of `O.type` if
`O` is a module.
SI-7775 Harden against the shifting sands of System.getProperties

If another thread writes a new system property (which can happen
in pretty innocuous code such as `new Date`!), the compiler startup
could fail with a `ConcurrentModificationException` as it iterated
all bindings in the properties map in search of a boot classpath
property for esoteric JVMs.

This commit uses `Properties#getStringProperties` to get a snapshot
of the keys that isn't backed by the live map, and iterates these
instead. That method will also limit us to bindings with String
values, which is all that we expect.
Merge pull request #2871 from retronym/ticket/7779

SI-7779 Account for class name compactification in reflection
Merge pull request #2868 from retronym/ticket/7775

SI-7775 Harden against the shifting sands of System.getProperties
[nomaster] SI-7790 No ScriptEngine in 2.10 build

The service entry was inadvertendly added in
`e3b5e0ba40447970d621cfeed5cc1770df69884f`,
"Sanity for build.xml: exscriptus&positus delendus est,"
which is ant latin for: "Reduced copy/pasting to the best
of my antabilities."

With that degree of hubris, it was inevitable that the
commit introduced a copy/paste bug.  What is the Attic
Greek for copy/paste?

I'm pretty sure that in fifth century Athens they would
just pound one inscription to rubble using a bigger
inscription. They had slaves for that kind of work.
You never hear about Socrates tweaking the build script.
That's the reason he never wrote anything down.
Commit .gitignore directly

Rather than relying on the cloner to copy the
provided gitignore.SAMPLE files.

This finishes the job started in c48509598, mostly
by reverting that commit and moving the two existing
SAMPLE files to the final destinations.

Use `.git/info/exclude` to augment the list of patterns
with entries specific to your workflow.
(cherry picked from commit b51cb581270da7021b2ea122dc059847101d56a7)

==============================================
Paring back the scope of our shared .gitignore

Importantly, limit the exclusion of build.properties
to the file in the root directory, paving the way for
the return of an SBT build.

  - Unignores .bak, .jar, and ~
  - limit ignorance of qbin to the root directory

.log files, generated by partest, are still ignored.

To see ignored files in your workspace, try:

    git ls-files --others --ignored --exclude-standard -- test | grep log
    git status --ignored -- test
(cherry picked from commit f0bbd2ca32acb40be37dc382c1f95081deca3f22)
Merge pull request #2897 from retronym/backport/gitignore

[backport] Commit .gitignore directly
Merge pull request #2891 from som-snytt/issue/7790-no-scriptengine

SI-7790 No ScriptEngine in 2.10 build