Backports the text rendering code from 1.6 to 1.5.
Done by starting with the current master's engine/render/text_render
and backporting things as-needed until it worked.
CLX rendering and text input handling are also backported as part of
this change.
* Use explicit typecasts to force signed char comparisons
Avoids warnings about tautological comparisons (either the >= 0 comparison for ARM/PowerPC or the <= 127 comparison for x86*)
* Remove unused function
Gleb Mazovetskiy
Cesar Canassa
Andrew James
Anders Jenbo