Add a test for the Branch header being in hg export.

tests/test-impexp-branch

@@ -0,0 +1,39 b''
+#!/bin/sh
+
+cat >findbranch.py <<EOF
+import re, sys
+
+head_re = re.compile('^#(?:(?:\\s+([A-Za-z][A-Za-z0-9_]*)(?:\\s.*)?)|(?:\\s*))$')
+
+for line in sys.stdin:
+    hmatch = head_re.match(line)
+    if not hmatch:
+        sys.exit(1)
+    if hmatch.group(1) == 'Branch':
+        sys.exit(0)
+sys.exit(1)
+EOF
+hg init a
+cd a
+echo "Rev 1" >rev
+hg add rev
+hg commit -m "No branch."
+hg branch abranch
+echo "Rev  2" >rev
+hg commit -m "With branch."
+if hg export 0 | python ../findbranch.py; then
+    echo "Export of default branch revision has Branch header" 1>&2
+    exit 1
+fi
+if hg export 1 | python ../findbranch.py; then
+    :  # Do nothing
+else
+    echo "Export of branch revision is missing Branch header" 1>&2
+    exit 1
+fi
+# Make sure import still works with branch information in patches.
+cd ..
+hg init b
+cd b
+hg -R ../a export 0 | hg import -
+hg -R ../a export 1 | hg import -

tests/test-impexp-branch.out

@@ -0,0 +1,2 b''
+applying patch from stdin
+applying patch from stdin