[TopGit PATCH 2/2] tg-create.sh: Introduce topgit.subjectprefix config option

[Bert Wesarg <bert.wesarg@googlemail.com>]

Set the topgit.subjectprefix config option to prepend the string to the [PATCH]
field in the Subject: line of the '.topmsg' file.

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>

---
 README       |    7 ++++---
 tg-create.sh |    3 ++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/README b/README
index bd4f17a..f821bab 100644
--- a/README
+++ b/README
@@ -204,9 +204,10 @@ tg create
 
 	After `tg create`, you should insert the patch description
 	to the '.topmsg' file, which will already contain some
-	pre-filled bits. You can set topgit.to, topgit.cc and topgit.bcc
-	configuration variables in order to have `tg create`
-	add these headers with given default values to '.topmsg'.
+	pre-filled bits. You can set topgit.subjectprefix, topgit.to,
+	topgit.cc and topgit.bcc configuration variables in order to
+	have `tg create` use this subject prefix and add these headers
+	with the given default values to '.topmsg', respectively.
 
 	The main task of `tg create` is to set up the topic branch
 	base from the dependencies. This may fail due to merge conflicts.
diff --git a/tg-create.sh b/tg-create.sh
index 0bf329c..c2b38bf 100644
--- a/tg-create.sh
+++ b/tg-create.sh
@@ -107,7 +107,8 @@ author_addr="${author%> *}>"
 	! header="$(git config topgit.to)" || echo "To: $header"
 	! header="$(git config topgit.cc)" || echo "Cc: $header"
 	! header="$(git config topgit.bcc)" || echo "Bcc: $header"
-	echo "Subject: [PATCH] $name"
+	subject_prefix="$(git config topgit.subjectprefix)" && subject_prefix="$subject_prefix "
+	echo "Subject: [${subject_prefix}PATCH] $name"
 	echo
 	cat <<EOT
 <patch description>
-- 
tg: (2fc069d..) t/subject-prefix (depends on: t/fix-subject-line-in-.topmsg)