[PATCH] textproc/bsdgrep: Update to 2.6.0 and set LICENSE

The following list of changes are roughly what has occurred since the last
update:

Features:

• With bsdgrep -r, the working directory is implied if no directory is specified
• bsdgrep will now behave as bsdgrep -r does when it's named rgrep
• bsdgrep now understands -z/--null-data to use \0 as EOL
• GNU regex compatibility is now indicated with a "GNU compatible" in the version string

Fixes:

• --mmap no longer hangs when coming across an EOF without an accompanying EOL
• -o/--color matching generally improved, now produces earliest / longest matches
• Context output now more closely aligns with GNU grep
• Zero-length matches no longer exhibit broken behavior
• Every output line now honors -b/-H/-n flags

Other fixes are also present.

While here, move to the version as reported by grep -V -- I intend to bump
the version in base sensible as bugfixes/features roll in.

Tested with: Poudriere (amd64, head)
Tested with: Poudriere (amd64, 11.1)
Tested with: Poudriere (amd64, 10.4)
Glanced at by: Portlint -AC
PR: 227639, 197531
Approved by: portmgr (feld)