check_msg.c: make open_tmp_file not static
check_msg.c: make open_tmp_file not static

The pack unit tests will need to have a way to create a
temporary file. Allowing them to use open_tmp_file is
simpler.

git-svn-id: ae38cf1093b87151f738d2b2220cac7742ad2e55@963 64e312b2-a51f-0410-8e61-82d0ca0eb02a

lubosz/check,lubosz/check,lubosz/check,lubosz/check