Changed OpenGL support for the Mac OS X platform: use cocoa instead of deprecated AGL.
All changes are mac-specific, except a very minor change in file src/gl_draw.cxx
where string drawing wrongly claimed to support @symbol, not possible
because symbols are drawn using non-GL primitives.

Unchanged application code can use the new FLTK code.
In addition, the new code allows mac applications to draw OpenGL scenes
at high resolution on so-called 'retina' displays, but this requires some
support from app code. They must call, before opening GL windows,
Fl::use_high_resolution(1);
and change their glViewport() calls as follows
glViewport(0, 0, pxel_w(), pixel_h());
This uses 2 new member functions of the Fl_Gl_Window class,
pixel_w() and pixel_h() returning the window dimensions in pixel
units, that is, twice the w() and h() when the window is mapped
on a retina display.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10498 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Removed use of AGL framework

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10499 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Function imgProviderReleaseData() is made apple-specific.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10500 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Removed compilation warning when compiling fluid/file.cxx on apple.
Also, added explanatory comment of the purpose of a GNUC-specific
attribute in FL/fl_ask.H

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10501 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Removed the Xcode3 directory altogether because Xcode3 is very old
and because Xcode3 opens very well the Xcode4 ide anyway.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10502 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Added documentation about the new support for high resolution OpenGL graphics
on Apple retina displays.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10503 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Remove the link error sometimes caused by class Fl_XFont_On_Demand not exported from libfltk.so but called 
by function gl_font() of file src/gl_draw.cxx (X11-specific).

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10504 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Fix typo in Fl_cocoa.mm if the ABI was set to 10304 or greater.
Seems ot be compiling OK again now.



git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10505 ea41ed52-d2ee-0310-a9c1-e6b18d33e121