Removed GSL dependency. Gmsh now uses blas and lapack for linear algebra
stuff.

what was causingthe uncomprehensible LNK1179 error ("duplicate
COMDAT") with MSVC.

No idea why.

moved all string options to std::string

*****************************************************************
WARNING: this has the potential to break things in subtle ways...
         PLEASE TEST AND REPORT ANY WEIRDNESSES
*****************************************************************

get string option would NEVER work! Ugly fix until will replace all const char*
with std::strings in the options

* point not found should NOT be an error in the octree

easy way to apply this to mesh/views unless we duplicate vertex arrays
anyway

Added "File->Save Options" to automatically save options for the
current project (same name + appended ".opt")

OpenProject will detect the ".opt" and will load the options
automatically if available.

Adapted from an original idea and patch from <jiri.hnidek@tul.cz>.

Thanks Jiri!

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

that the 2 steps are orthogonal
* added full-hexa subdivision algo