Merge pull request #17 from pbosetti/master

Changed logic for rake file when compiling included gems
Fix for compiling bundled gems when libmruby.a depends on external dynamic libs.
Also works with VisualStudio compiler/linker
Merge pull request #18 from pbosetti/master

Partially solved regression introduced in last commit.
Merge pull request #19 from pbosetti/test

Fix for libmruby.a depending on dlls
Fix build