Build OpenSSL for Ruby 2.0 on OS X.

Apple ships a patched, incompatible OpenSSL. We build a compatible
OpenSSL from source.
Add PACKAGE_{CONFIGURE,MAKE}_OPTS_ARRAY for injecting quoted arguments
Extract `package_option` helper
Default CC=cc for broken Ruby 2.0 gcc detection on OS X
Quote `$PREFIX_PATH`
We use `uname -s` to test for OS X elsewhere; stay consistent
Guard against missing openssl (future OS X versions?)
Handle 32-bit OS X
Remove OpenSSL note in the readme
Explicitly declare OpenSSL condition and URL in the definition files
Merge master
Use $RUBY_BIN
Be sure to use c_rehash from the OpenSSL build we just installed
Rely on OpenSSL to pick the right arch. Hint that we prefer 64-bit.
Support conditional package installation with `--if <test>`
Include certs from /System/Library/Keychains/SystemRootCertificates.keychain