Trunk build would fail due to the nonexistence of zaptel hwgain

structures missing. Patched configure to check for this stuff and
put a #ifdef around the offending code in chan_zap. Thanks to file
for overseeing this.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@92422 65c4cc65-6c06-0410-ace0-fbb531ad65f3