MFC	r275531, r275581, r275582;

patch(1): Small changes to sync with OpenBSD

Update OpenBSD CVS revision tag for our r255232.
Prefer setvbuf() to setlinebuf().
Small space changes, mostly to keep in sync with OpenBSD

Obtained from:	OpenBSD
MFC	r275553, r275612;

patch(1): Bring fixes from OpenBSD

Check fstat return value.  Use off_t for file size and offsets.
Avoid iterating over end of string.

Introduce strtolinenum to properly check line numbers while parsing:
no signs, no spaces, just digits, 0 <= x <= LONG_MAX

Properly validate line ranges supplied in diff file to prevent overflows.
Also fixes an out of boundary memory access because the resulting values
are used as array indices.

PR:		195436
Obtained from:	OpenBSD