-complete the doc of the GSHHS Plugin
-compile GSHHS plugin even if matheval is not present

HAVE_XXX defines.

This fixes three longstanding problems:

- the API was hard to use because some headers had HAVE_XXX ifdefs, so
  that cient codes had to know how the lib was compiled to compile
  themselves

- we had to do make clean after each ./configure, which erased too
  much (e.g. most of contrib)

- make depend could include unwanted stuff since it redefined FLAGS

added File->Clear + changed behaviour of File->New (now just adds a
new model)

allow smaller fonts for palettes (test with "-deltafontsize")

use display list for 3d arrows (approx. 2x speedup on my laptop for
large vector views) and spheres

removed static quadrics (wrong when \exists multiple gl contexts),
replaced with correct(?) init in drawContext

- fix bb computation to avoid model jumping around when adding points in z=0 plane
- pass interpol matrices as ref

window with experimental tree browser

changed -part command line handling

workaround faulty fltk installs (e.g. in current Debian or Ubuntu)

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

multi-window & multi-coordinate system drawing.

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

cleanup high order

- don't die silently when a read function fails
- fixed while bunch of compiler warnings

- fixed missing getShapeFunction/getGradShapeFunction + return all sf
  at once so we can implement MElement in term of these consistently
  (w or w/o FunctionSpace)

- can now merge multiple meshes and remove duplicate mesh vertices
  (useful e.g. when merging several STLs)

- added easy interface to create model-based postpro datasets on the
  fly + use this for mesh quality stats