Add log.abbrevCommit config variable

Add log.abbrevCommit config variable as a convenience for users who
often use --abbrev-commit with git log and friends. Allow the option
to be overridden with --no-abbrev-commit. Per 635530a2fc and 4f62c2bc57,
the config variable is ignored when log is given "--pretty=raw".

(Also, a drive-by spelling correction in git log's short help.)

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/revision.c b/revision.c
index a7cf79b..be74bf9 100644
--- a/revision.c
+++ b/revision.c
@@ -1429,6 +1429,9 @@
 			revs->abbrev = 40;
 	} else if (!strcmp(arg, "--abbrev-commit")) {
 		revs->abbrev_commit = 1;
+		revs->abbrev_commit_given = 1;
+	} else if (!strcmp(arg, "--no-abbrev-commit")) {
+		revs->abbrev_commit = 0;
 	} else if (!strcmp(arg, "--full-diff")) {
 		revs->diff = 1;
 		revs->full_diff = 1;