pbx: Fix regression caused by taking advantage of the function name sort.

Taking advantage of the sorted order of the registered functions container
requires that they are actually inserted in the expected sort order.

* Insert the registered functions into the container in case sensitive
position.  As a result, only the complete_functions() routine needs to
search the entire container because it does a case insensitive search for
convenience.

Caught by the unit tests.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381118 65c4cc65-6c06-0410-ace0-fbb531ad65f3