am: learn passing -b to mailinfo

git-am could pass -k to mailinfo, but not -b.  Introduce an option
that does so.  We change the meaning of the 'keep' state file, but are
careful not to cause a problem unless you downgrade in the middle of
an 'am' run.

This uncovers a bug in mailinfo -b, hence the failing test.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-am.sh b/git-am.sh
index 6cdd591..8b755d9 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -15,6 +15,7 @@
 s,signoff       add a Signed-off-by line to the commit message
 u,utf8          recode into utf8 (default)
 k,keep          pass -k flag to git-mailinfo
+keep-non-patch  pass -b flag to git-mailinfo
 keep-cr         pass --keep-cr flag to git-mailsplit for mbox format
 no-keep-cr      do not pass --keep-cr flag to git-mailsplit independent of am.keepcr
 c,scissors      strip everything before a scissors line
@@ -345,6 +346,8 @@
 		utf8= ;;
 	-k|--keep)
 		keep=t ;;
+	--keep-non-patch)
+		keep=b ;;
 	-c|--scissors)
 		scissors=t ;;
 	--no-scissors)
@@ -522,16 +525,25 @@
 	fi
 esac
 
+# Now, decide what command line options we will give to the git
+# commands we invoke, based on the result of parsing command line
+# options and previous invocation state stored in $dotest/ files.
+
 if test "$(cat "$dotest/utf8")" = t
 then
 	utf8=-u
 else
 	utf8=-n
 fi
-if test "$(cat "$dotest/keep")" = t
-then
-	keep=-k
-fi
+keep=$(cat "$dotest/keep")
+case "$keep" in
+t)
+	keep=-k ;;
+b)
+	keep=-b ;;
+*)
+	keep= ;;
+esac
 case "$(cat "$dotest/keepcr")" in
 t)
 	keepcr=--keep-cr ;;