contrib/coccinelle: add basic Coccinelle transforms

Coccinelle (http://coccinelle.lip6.fr/) is a program which performs
mechanical transformations on C programs using semantic patches.  These
semantic patches can be used to implement automatic refactoring and
maintenance tasks.

Add a set of basic semantic patches to convert common patterns related
to the struct object_id transformation, as well as a README.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/coccinelle/README b/contrib/coccinelle/README
new file mode 100644
index 0000000..9c2f887
--- /dev/null
+++ b/contrib/coccinelle/README
@@ -0,0 +1,2 @@
+This directory provides examples of Coccinelle (http://coccinelle.lip6.fr/)
+semantic patches that might be useful to developers.