"Fix" file mode for windows vagrant installs

all files in windows+vagrant shared folders are marked as executable and git tries to commit this change. ARGH.

this makes a config change in each git repository in the shared folder, after initial deploy, that makes git ignore file perms.  we check to make sure the box is vagrant+windows before doing anything, so linux/mac vagrant instances are unaffected.

this slightly sucks because windows users, without some explicit options to git commit, won't be able to save permissions changes to scripts.