.gitignore: add coverity, patches and special ignore

 - coverity stands for coverity scanner results
 - .pc for quilt
 - .git-ignore directory for various things which
   are not supposed to be in repo, just for convenience

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

.gitignore

@@ -7,6 +7,9 @@ _CPack_Packages
 *.gcda
 *.gcov
 patches/
+.git-ignore/
+.pc/
+coverity/
 coverage/
 coverage.info
 *.o