Add "git-patch-id" program to generate patch ID's.

A "patch ID" is nothing but a SHA1 of the diff associated with a patch,
with whitespace and line numbers ignored.  As such, it's "reasonably
stable", but at the same time also reasonably unique, ie two patches
that have the same "patch ID" are almost guaranteed to be the same
thing.

IOW, you can use this thing to look for likely duplicate commits.

1 files changed, 2 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index e3405dc3a7..fd5c80f753 100644
--- a/Makefile
+++ b/Makefile
@@ -35,7 +35,7 @@ PROG=   git-update-cache git-diff-files git-init-db git-write-tree \
 	git-http-pull git-ssh-push git-ssh-pull git-rev-list git-mktag \
 	git-diff-helper git-tar-tree git-local-pull git-write-blob \
 	git-get-tar-commit-id git-mkdelta git-apply git-stripspace \
-	git-cvs2git git-diff-stages git-rev-parse
+	git-cvs2git git-diff-stages git-rev-parse git-patch-id
 
 all: $(PROG)
 
@@ -121,6 +121,7 @@ git-stripspace: stripspace.c
 git-cvs2git: cvs2git.c
 git-diff-stages: diff-stages.c
 git-rev-parse: rev-parse.c
+git-patch-id: patch-id.c
 
 git-http-pull: LIBS += -lcurl
 git-rev-list: LIBS += -lssl