Stretch freeswitch audio to match event timing

This helps maintain audio sync with video and events when freeswitch's
internal timing differs from red5's.
Convert timestamps to numbers for subtraction
Correct variable name to refer to original audio length
Use the old sox trim syntax for the version on ubuntu lucid
Merge pull request #228 from kepstin/stretch-audio-sync

Stretch freeswitch audio to match event timing (experimental)