When the input file name has no extension, just ignore the extension
    instead of failing outright. This is useful when /dev/stdin is the input
    filename and there are known to be no dependencies to deal with.
Allow pkg add to read from a pipe or a non-regular file -- so now, all
of the following work:

Installing portmaster-3.17.2... done

Installing portmaster-3.17.2... done

Installing portmaster-3.17.2... done

The special filename '-' means 'read from stdin', but should also read
from character special devices, pipes, fifos, unix domain sockets etc.
Update man page to descripe the special '-' filename meaning 'read
from stdin' and better describe the behaviour when the base directory
for packages cannot be intuited from the filename passed on the
command line.