Style. Parentheses are not required here.
Style. Remove unnecessary whitespace.
Fix JRuby exception in posix run! method.

Works for jruby-1.7.9 in both 1.8 mode and 1.9 mode.

Fixes #161.
Include RubySL for Rubinius.
Upgrade Travis config for Rubinius.

The -18mode/-19mode syntices are no longer supported.
Fix ruby-1.8.7 breakage.
Introduce a runtime cache into the environment.

It is a general-purpose runtime cache scoped to the environment instance. It is not persisted anywhere. One use case is to avoid repeating an expensive operation across multiple instances of the same class.
Add missing require.
Refactor: avoid stubs in tests.
Some introductory functional tests on the git source.
Fix ruby-1.8.7 breakage.