When we call a gosub routine, the variables should be scoped to avoid contaminating the caller.

This affected the ~~EXTEN~~ hack, where a subroutine might have changed the
value before it was used in the caller.
Patch by myself, tested by ebroad on #asterisk


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@222273 65c4cc65-6c06-0410-ace0-fbb531ad65f3