re-fix Field.h API dependency

fix shift/conflict reduce in parser introduced by Field stuff

make parser embeddable in code with other parser (yy->gmsh_yy)
more work on headers
fixed lots of gcc warnings

start reducing header pollution (removed Gmsh.h + cleaned up GModel & co)

simplify Visual C++ stuff: removed hacks from configure and created
template "variables" file (so that building with msvc only requires
gnu make)

	-) A bug has been corrected in the MeshAdapt Procedure
	-) The 2D Delaunay is now Anisotropic
	-) 3D Sliver removal procedure has been improved
	-) Curvilinear mesh generation has been slightly improved,
	   even if it is still far from done
JFR

Removed the "search around point" strategy when we provide a background mesh.

(Now that we can have several fields, it's much better to specify another default
field for when a search fails.)

moving to new post-processing database

                    *** WARNING ***

do not upgrade if you need plugins or adaptive views: these have not
been ported (yet) to the new database

                    *** WARNING ***

- only save mesh vertices that are used by elements

- fix warnings + indent + memory leaks in new Field classes

- temporary fix to avoid crashes in new field manager when post-pro
  views are reloaded or removed at run-time