Add support for "or later" variants of all GNU licenses.
Now you can use, for example,

LICENSE=  GPLv2+

instead of incorrect

LICENSE=  GPLv2 GPLv3

or inaccurate and not machine readable

LICENSE=  GPLv2 # or later

Also add some categorization to licenses list and fix some
whitespace problems in bsd.licenses.db.mk

Approved by: portmgr (bapt)
Differential Revision: D4148