games/nehquake: unbreak, undeprecate, and assume maintainership

Define LICENSE (GPLv2 or later), add missing USE_XORG components,
do not allow ``make build'' to succeed when compilation actually
fails, bump MAX_PRINTMSG value to accommodate long GL extensions
string returned by modern video cards, amend post-install advice.

Tested on: 13-STABLE/i386 + ATI Radeon HD 4350 (RV710)