This patch adds a new api call:

int pbx_builtin_serialize_variables(struct ast_channel *chan, char *buf, size_t size);
takes a chan and a char * 'buf' assumed to be 'size' bytes.

The function fills 'buf' with a <CR>('\n') delimited list of name,value pairs in turn delimeted by '='
eg:
SIPCALLID=f30e4e72-f715193f@1.2.3.4
SIPUSERAGENT=Sipura/SPA2000-2.0.6(c)
SIPDOMAIN=1.2.3.4

It returns the acutal number of variables encountered.
If the attempt to fill 'buf' goes beyond 'size' bytes the operation is halted and the incomplete string is returned as is.

To demonstrate a use for this, the "show channel <channame>" command has been retrofitted with the call so it also dumps all of the chan's vars

*CLI> show channel Zap/5-1
 -- General --
           Name: Zap/5-1
           Type: Zap
       UniqueID: 1098480666.17
      Caller ID: 4999
 Caller ID Name: Tony
    DNID Digits: (N/A)
          State: Up (6)
          Rings: 0
   NativeFormat: 68
    WriteFormat: 4
     ReadFormat: 4
1st File Descriptor: 22
      Frames in: 41969
     Frames out: 83240
 Time to Hangup: 0
   Elapsed Time: 0h13m54s
 --   PBX   --
        Context: phone1
      Extension: 4994
       Priority: 2
     Call Group: 2
   Pickup Group: 2
    Application: Dial
           Data: IAX2/ulaw@cube1/00010014994@croip
          Stack: 0
    Blocking in: ast_waitfor_nandfds
Variables:
DIALEDPEERNUMBER=ulaw@cube1/00010014994@croip
DIALEDPEERNAME=IAX2/cube1/3
CALLTYPE=SPEECH
tempvar=tempval


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@4051 65c4cc65-6c06-0410-ace0-fbb531ad65f3