This is required to avoid name conflicts with the Cocoa libraries
on OS X.
I renamed the `class SolveSpace` to `class SolveSpaceUI`, because
that's what it does, and because otherwise the namespace would
have to be called something else than `namespace SolveSpace`.
This will allow solvespace to run on pre-OpenGL 3.0 implementations,
such as VirtualBox (and possibly others).
However, VirtualBox's handling of framebuffer objects is buggy;
it tries to draw over our X window and fails to do either.
I hate OpenGL.
Apparently pbuffers are also a deprecated and unportable
way of offscreen rendering. They're not supported by
Chromium OpenGL implementation, which is what 3D-accelerated
VirtualBox uses.
This would also help a future OS X port.
In principle, GTK3 is the way forward, and GTK2 is officially
deprecated, though still maintained. In practice however, GTK3
is often unbearably buggy; e.g. on my system, combo boxes
don't ever roll up in GTK3 windows. So I have added support
for both.
This required a few minor changes to the core, namely:
* GTK wants to know beforehand whether a menu item is a check
menu item or a regular one.
* GTK doesn't give us an easy way to execute something after
any event is processed, so an explicit idle timer is added.
This is a no-op on Win32.
* A few function signatures were const'ed, since GTK expects
immutable strings when converting to Glib::ustring.
fltkutil.cpp should be independent of FLTK so that it can be linked
into libslvs while neither requiring every user of the library to
reimplement these support routines nor requiring linking in FLTK.
