Add definition for heroku-patched 1.8.7-p375

This build is an unofficial backport of the patch for
"Heap Overflow in Floating Point Parsing (CVE-2013-4164)"
to Ruby 1.8.7-p374.

The defnitoin refers to a tarball of this tag:
https://github.com/heroku/ruby/releases/tag/v1_8_7_375
Merge pull request #463 from cheerful/heroku-1.8.7-p375

Add definition for heroku-patched 1.8.7-p375
1.9.3 builds with performance patches.
Build for 1.9.3-p385-perf.
Build for 1.9.3-p392-perf.
Build for 1.9.3-p429-perf.
Build for 1.9.3-p448-perf.