Use Homebrew libyaml if it is available

This checks for Homebrew's yaml to see if it
is available and that `--with-libyaml-dir` hasn't
been specified.

Related issue: #379
Fix Rubinius gem binstubs path

Rubinius 2 insists that it installs RubyGems binstubs into
`PREFIX/gems/bin` instead of `PREFIX/bin`.

This creates complexity for rbenv rehash and exec processes, so we
symlink `gems/bin` into `bin` and have RubyGems create binstubs at a
location that is consistent with other Ruby implementations.

See sstephenson/rbenv#178, sstephenson/rbenv#461
Merge pull request #432 from ProGNOMmers/rbx-2.1.1

Add rbx-2.1.1
Added a definition for JRuby 1.7.6.
Merge pull request #435 from nirvdrum/jruby-1.7.6

Added a definition for JRuby 1.7.6.
Fix Rubinius 2.1.x on Linux by supporting bz2 archives

`tar` on OS X auto-detects the type of compression used, so it doesn't
care whether `-z` or `-j` flags were passed to it for extraction.
However, since latest Rubinius archives are compressed with bzip2, we
must handle this distinction explicitly for the sake of other platforms.

fixes #470
Merge pull request #433 from sstephenson/rbx-fix

Fix Rubinius gem binstubs path
Fix broken test suite

Fixes breakage caused by curl arguments change in
d0912e4fb550490423af42954b715be2f15370ec
configure Travis CI
ruby-build 20131024
Keep mirror up-to-date using Travis CI

When new Ruby definitions get added, our current CloudFront mirror may
get out of date. This adds a task to the CI process that detects
added/changed package URLs and uploads them to our S3 bucket.

Fixes #392, references #395
Fix detecting changed definitions in mirror script

Grep mustn't get invoked with 0 parameters, otherwise it will hang
waiting on stdin.
Merge pull request #438 from sstephenson/travis-mirroring

Keep mirror up-to-date using Travis CI
Merge master into docwhat-homebrew-yaml

Conflicts:
	share/ruby-build/1.9.1-p378
	share/ruby-build/1.9.1-p430
	share/ruby-build/1.9.2-p0
	share/ruby-build/1.9.2-p180
	share/ruby-build/1.9.2-p290
	share/ruby-build/1.9.2-p318
	share/ruby-build/1.9.2-p320
	share/ruby-build/1.9.3-p0
	share/ruby-build/1.9.3-p125
	share/ruby-build/1.9.3-p194
	share/ruby-build/1.9.3-p286
	share/ruby-build/1.9.3-p327
	share/ruby-build/1.9.3-p362
	share/ruby-build/1.9.3-p374
	share/ruby-build/1.9.3-p385
	share/ruby-build/1.9.3-p392
	share/ruby-build/1.9.3-p429
	share/ruby-build/1.9.3-p448
	share/ruby-build/1.9.3-preview1
	share/ruby-build/1.9.3-rc1
	share/ruby-build/2.0.0-preview1
Have Rubinius 2 use libyaml from Homebrew if available
Simplify stubbing commands in tests

No more awkward juggling of PATH entries and preset stubs in version
control. Commands are stubbed by symlinking the main stub from a
temporary `$TMP/bin` directory that's added once to PATH in tests.
Prevent glob expansion in stub patterns

When stub patterns were broken down into an array, they were
accidentally subject to glob expansion. E.g., a pattern '*' might expand
to whatever is in the current directory. This is unwanted, as we need to
preserve patterns as-is.
Add tests for Homebrew libyaml integration
Merge branch 'docwhat-homebrew-yaml'

Use Homebrew libyaml if available.

Closes #381
Remove non-portable `ln -h` flag

Works on OS X but fails on CI.