Necessary on cygwin, where uid_t and gid_t are 4-byte long rather
than int, causing gcc -Wformat warnings.

* src/util/util.c (virFileOperationNoFork, virDirCreateNoFork)
(virFileOperation, virDirCreate, virGetUserEnt): Cast uid_t and
gid_t before passing to printf.
* .gitignore: Ignore Windows executables.