config.c: fix writing config files on Windows network shares
config.c: fix writing config files on Windows network shares

Renaming to an existing file doesn't work on Windows network shares if the
target file is open.

munmap() the old config file before commit_lock_file.

Signed-off-by: Karsten Blees <955b63282c975ba379c4995cac1c2e1e7dfebe62@dcon.de>
Acked-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Acked-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git