libc: Document some more *_l() functions.

mbrtowc_l()
mbsinit_l()
mbstowcs_l()
mbtowc_l()
ungetwc_l()
wcrtomb_l()
wcsftime_l()
wcstombs_l()
wcswidth_l()
wctomb_l()
wcwidth_l()
libc: Remove documentation for strtoq_l() and strtouq_l().

They are not provided and I was misled by xlocale.3 listing them.
Fix this too.
libm: cacos(3) character magic zapped

Assisted-by: swildner
bsd.man.mk: change `mandiff' from groff to nroff

The cacos(3) incident showed that groff(1) output is not to
be trusted.  Use nroff(1) instead.  2575 -> 2565.