use UTFmax and Runemax for documentation
instead of the constants 3 and 0xffff.  in a few
cases Runeerror was still mistakenly 0x80.

the files /sys/src/cmd/postscript/common/rune*
should be removed.

20091128 i realized that i included the function
"isdigitrune" by mistake in /sys/include/libc.h in
this submission.