we have already updated autoconf to use configure.ac instead of
configure.in, so update release.sh to use the new name.
Change-Id: I2dc2beaf2f85058c4627183bc093052677ccba1b
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/537
Tested-by: jenkins