fix regression with extrusions of many surfaces: order faces by tag - this allows to minimize the number of passes necessary to resolve dependencies (otherwise 10 passes is not enough!)

natural convection added in the incompressible code

a frame solver is made
changed INRIA MESH output
removed feaure in BL field
started to do MNT diagrams
 

Major work on GUI : removed much-hated "menu window" & merged onelab tree in graphic window. Gmsh now requires FLTK 1.3.

(Additional changes: fixed crash when de-minimizing opengl window on mac os ; refactored Msg::StatusBar)

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     boundary layers in 2D 
     periodi bug fixed
     many other stuff

JF