Port over a bunch more transcoding stuff + gzip encoding logic.
Patch up things that broke from my mega-port.

* GzipReader#read always returns ASCII-8BIT strings when given a
  length.
* String#encode needed some ported logic to fit other pieces.
* Get ECONV constants propagated into RubyConverter.
* Encoding 7-bit strings from/to ASCII-compat encs is a no-op.
Large port of MRI IO transcoding logic, to fill in our gaps.
Fixes and a few additional ports to get test:mri19 green.

Additional fixes to get test:mri18 green.
Edging closer to everything passing again.
Use normal "new" logic in Regexp. Fixes #955.
Set `jruby.jit.exclude` method to `''`.

The old default `none` prevents a method named `none` to be
JIT-compiled.

Fixes #954.
Remove mention of .jrubyrc for C Extensi building [skip ci]

Fixes #953
Enabling C Extensions via `.jrubyrc` is not effective for building gems,
so remove the mention of it to avoid confusion.
Change `--properties` output for null default opts [skip ci]

Fixes #949

For options whose default is `null`, it is confusing to print out the
string `null`, since it is not a likely value that the user can use.
While the message makes it clear that the value will be interpreted as a
String, it is a good idea to leave it blank instead, so that the user
can fill it themselves.
added some note about maven version
fix parent-pom for jruby-jars
added snapshot repo for plugins
added missing dep to reactor
expose JRubyJars::VERSION with loading gem
Use 'let' in code, and fix spec description

Avoid hard coding reused value.
Fix spec description text
Fixes to get all 1.9 specs passing again.
IR Experimental: call-site profiling that feeds into inlining

* Added experimental call-site profiling in the IR interpreter
  and used it to drive inlining decisions.

  On bench_richards about ~7% speedup (~9% fewer instrs)
  On red_black_tree, about ~10% slowdown (~10% more instrs)

  To be investigated and experimented with more.
  Committing so others can partake of the fun as well.
Two steps forward, one step back. Re-fix unit test failures.
Merge remote-tracking branch 'origin'