Fix for compilation under Win/MinGW
Made compatible with VisualStudio
Merge branch 'master' of https://github.com/iij/mruby-io
Now the drive letter is returned as leading path element  by File#dirname on Windows
Updated mrb_include_module call after mruby 1.0.0
Merge branch 'master' of https://github.com/iij/mruby-io into test

Conflicts:
	src/io.c
Added File.foreach method.
Improved error management in File.new (Errno can be undefined)
Fixed bug in File.expand_path() on Windows (forever recursive loop)
Merge pull request #11 from pbosetti/master

Can build on VisualStudio, revised.