MFC r311739:

Use SRCTOP instead of spelling out the full path with .CURDIR

This helps condense the output for CFLAGS and .PATH

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Get rid of libl dependency. We needed it only to provide yywrap. But
yywrap is not necessary when parsing a single hast.conf file.

Suggested by: kib
Reviewed by: pjd

Move snmp_hast manual to section 3, where all other manual pages for
bsnmp modules are located.

Section 3 (Library Functions) looks wrong for this manual page, which
contains only module description, that is why initially it was located
to section 8 (System Manager's Manual). On the other hand manual
pages for all other bsnmpd modules are already located in the section
3, and having all pages in one section looks more consistent. Also,
currently, similarly to manuals for other modules, snmp_hast manual
contains LIBRARY section, which is not good style for section 8.

Requested by: joel
X-MFC with: r250379

HAST module for bsnmpd(1).

Reviewed by: harti, pjd
MFC after: 2 weeks