- now that the frame buffer stores its render time, the 'ms' return from I_GetTimeFrac is not needed anymore, we may just as well use the globally stored value instead.
The only feature this value was ever used for was texture warping.
Since this calls I_WaitVBL, which resets the frame time, it was essentially just like calling a real-time timer anyway and nothing in it required a specific 0-timepoint.
The same applies to the ZScript interface. All it needs is a millisecond-precise timer with no semantics attached.
- moved timer definitions into their own header/source files. d_main is not the right place for this.
- removed some leftover cruft from the old timer code.
