Added patch-all-projects command

Hi,

Thanks for posting these commands. I really like the idea of managing all my patches in a single makefile. I've added a command ('patch-all-projects') that takes the path to a patchfile as an argument, and patches each project contained within. The idea here is that a client could run a single drush command and have all their contrib modules patched instead of delivering a bunch of patches that they have to apply individually. Let me know what you think.

Best,
-Mike