[Asterisk-Dev] CVS HEAD file version tags and header include order

[Kevin P. Fleming]

Based on the discussion on this list today, I've added file version tags 
to all C source files in CVS HEAD, along with a 'show version files' 
command that can be used to display them.

Along the way, I converted all remaining files to include system headers 
before Asterisk headers and local headers; this may break builds on 
non-Linux platforms. If you find that it does, please don't report that 
"it's broken", but try to determine exactly what is the reason a 
particular system header needs to be included _after_ an Asterisk 
header. That way we can add the appropriate comments (or an alternative 
fix) when correcting the problem.