Add ability to build 1.8.7

Without this patch we're only building one configuration of Ruby for
crossfader.  There is not 1.8.7 version, only 1.9.3.  This is a problem
because we need to develop on 1.8.7 in some cases.
Build all crossfader configurations
Replace unpacked ruby-1.8.7-p371 with tarball
Move packages into pkg/ for artifact archives

Without this patch we're not archiving the build artifacts that result
from building all of the ruby packages.  This patch moves all of the
packages into the pkg/ directory after building them.  This makes it
easy to use an archive artifact rule of `pkg/*.pkg`.
Add ruby-2.0.0-p247 build
Reset src tree fully before each crossfader build
Synthesize packages into one archive
Add Mac OS X version to package version