Replace unifont with CFont and CFontManager, since the h_mgr interface
was
needlessly inconvenient.
Load the font textures through CTextureManager, to support dynamic
reloading (e.g. when resetting GL state - see #741).
Add CFontMetrics as a convenient wrapper for code that just wants to
measure text.
Fixes#1117.
This was SVN commit r14016.
