refactoring + removed periodic mesh specification from GEO_Internals : we now directly sync and use GModel

this is the way we should/will treat all extra tag-based attributes, not directly linked to a specific CAD kernel

Onelab "changed" flag is now multi-level (not just true/false). This allows finer granularity for complex clients. For example, Gmsh now responds to 4 levels of "changed"

- changed == 0: nothing to do
- changed == 1: only save the mesh (useful if we only chanaged some physical groups)
- changed == 2: only remesh and save the mesh (useful if we only changed some meshing paramaters)
- changed >= 3: reload geometry, remesh and save the mesh

- removed onelab::region and onelab::function (they complexify the interface, but bring no additional value compared to onelab::string)
- removed ONELAB2 experiment
- made client/Model name persistent, and define Gmsh/Model name so that we can uncouple e.g. .geo/.pro pairs

* New ENABLE_COMPRESSED_IO option to enable on-the-fly IO with gzipped files (patch from Alexis Salzman)
* New PrintParserSymbols() to print workspace (currently in option window, for debugging puroposes)

Fopen deals with non-ASCII filename paths on Windows.

- fixed MED node ordering
- polished 64 bit Cocoa Mac OS X FLTK version
- updated copyright