freeswitch: immediately end the script if configure for makefiles fails
freeswitch: use the stable branch

Easier if it's pegged at a known stable version instead of
using master all the time and unknowingly using different versions
on different machines.
freeswitch: change FS_GIT_REPO to stash.freeswitch.org

Seems like the old URL is dead.
Merge pull request #125 from darylyu/fs_install_fixes

freeswitch: small fixes