Modernize some portions of the ports man page.
Stop documenting other operating systems's default patha

Approved by:	bcr (mentor)
MFcalloutng (r244249, r244306 by mav):
- Switch syscons from timeout() to callout_reset_flags() and specify that
precision is not important there -- anything from 20 to 30Hz will be fine.
- Reduce syscons "refresh" rate to 1-2Hz when console is in graphics mode
and there is nothing to do except some polling for keyboard.  Text mode
refresh would also be nice to have adaptive, but this change at least
should help laptop users who running X.

Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo, marius, ian, markj, Fabian Keil