instead of deleting existing build directories, take a backup of them
extract build directory backup in to its own method and added alot of error handling
Merge pull request #32 from ilude/build-backup

Instead of deleting existing build directory, take a backup of it when upgrading bills-kitchen
Merge pull request #33 from ilude/ruby-update

update ruby to 1.9.3-p392 and associated devkit. ...
update RUBYDIR environment variable to ruby-1.9.3-p392-i386-mingw32