rebase-am: explicitly disable cover-letter

If the user has a cover-letter configuration set to anything other
than 'false', 'git format-patch' may generate a cover letter, which
has no place in "format-patch | am" pipeline.

The internal invocation of format-patch must explicitly override the
configuration from the command line, just like --src-prefix and other
options already do.

Signed-off-by: Felipe Contreras <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: felipec

git-rebase--am.sh

@@ -31,8 +31,8 @@ else
 	rm -f "$GIT_DIR/rebased-patches"
 
 	git format-patch -k --stdout --full-index --ignore-if-in-upstream \
-		--src-prefix=a/ --dst-prefix=b/ \
-		--no-renames $root_flag "$revisions" >"$GIT_DIR/rebased-patches"
+		--src-prefix=a/ --dst-prefix=b/ --no-renames --no-cover-letter \
+		$root_flag "$revisions" >"$GIT_DIR/rebased-patches"
 	ret=$?
 
 	if test 0 != $ret