[Serusers] nathelper module in cvs updated

[Maxim Sobolev]

Folks,

I've just finished merging changes from our development version of
nathelper into the ser's cvs. The following changes were made:

- Don't apply contact address rewriting in SDP body if the original
  address is 0.0.0.0, which usially present in re-INVITEs and means
  that sender asks to temporarly suspend media session;

- save original address into the oldmediaip option in the SDP body,
  which is useful for debugging;

- fix contact URI parsing routine to understand those URIs in the
  form sip:<ip>:<port>, which is the case with URIs generated by the
  Windows Messenger;

- some style fixes and general diff reduction with our development
  version.

All nathelper users are encouraged to test it and report any problems
to me, since it is probably the version that will be delivered with
the next ser release.

Thanks!

-Maxim