Something I've been itching to do for a while now. A minor optimization in app_voicemail.

Since the dtable in base_encode always gets populated with the same values every time and never
changes, make it static and const and only initialize it once. Also, there's no reason to 
define BASEMAXINLINE twice, so remove the redundant #define.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@94593 65c4cc65-6c06-0410-ace0-fbb531ad65f3