Fix DAHDI/Zaptel incorrect FXO signaling status on module load

Changed from using putenv to setenv like the other one

mod_esl: New module.  Allow to Passtruth API command to a remote FS via ESL.  First api doesn't keep a persistant connection to farend server explaining the name single_esl.  Future version will include settings to keep connections alive for multiple performance

mod_abstraction: New module.  Currently implement API abstraction.  Allow to simplify/standarize API name.  Initially built for mod_voicemail_ivr.  Allow to use scripting language as VM Storage by binding an API with specific argument to an different api call like python and send to it argument initially provided.

mod_voicemail_ivr: Changed behavior of TIMEOUT/INVALID option.  Instead to check incode if it was the last attempt, set the event header IVR-Retry-Left to how many attempt are left.  Then we can just do this please try again check inside the phrase system.  We can also add prompt like "This is your last chance, Press 1 for new messages, 2 for ...." using this method.

mod_voicemail_ivr: Added a bunch of default prompt for future use once we get sound recorded.  In the mean time, having it in the code wont cause problem as long we don't define the phrase in the config file

mod_voicemail_ivr: Added a missing menu in the conf.xml config.  Also refactor nearly all the function name to something more standard.  Also tried to make the flow as simple as possible in the menu.c

mod_voicemail_ivr: Document example settings parameters.  This is open for discussion before being implemented

mod_voicemail_ivr:  BETA : An alternative voicemail IVR system.  It require an API provider for voicemail access that is currently provided by mod_voicemail vm_fsdb API so it can be used simultaneously with mod_voicemail IVR.  It currently try to resemble the normal FreeSwitch Voicemail experience.  The goal is to expand upon that experience without affecting everyone inproduction user experience.

This fix a out of bound memory write.
(normally unreachable with a real phone)