r272282:
Search for the nearest PORTSDIR where Mk/bsd.ports.mk exists, from .CURDIR.
This will only take effect if PORTSDIR is not set, as previously supported.
r272363:
Always resolve PORTSDIR to absolute paths using realpath(1).
r272383:
Revise r272363 by collapsing the tests into a for loop.
Relnotes: yes