generalized the solver interface to allow permanent listening on a
socket for whoever wants to connect (gmsh -listen)

the polling should also be less CPU hungry in this new version

next step is to add new commands to the protocol so that solvers can
directly transmit data to merge (geometry, mesh, etc.) in addition to
messages and filenames

trying to fix compile with old g++ 2.95

added check for socklen_t in configure script

- fixed the "unix socket name is one character short" problem on
MacOS and AIX. Unfortunately, this required the client code to be
slightly modified as well (and as a consequence, old versions of getdp
will for example not work with new versions of Gmsh on MacOs and
AIX). But it's better to do things "the right way" (TM) for people who
want to connect using different languages (Perl, Python).

- moved the GmshServer stuff in its own class

- added missing rules in parser makefile (so that the parser gets
  rebuilt automatically when one changes Gmsh.y or Gmsh.l)

tiny cleanup

copyright update

Update copyright notice

Move the client/server code to a more permissive X11-like license

Fix whitespace in copyright headers

Updated copyright