freemount-client:  Fix comments
freemount-client:  Recognize exec:// addresses
freemount-client:  Treat path as dir, not socket

Given a plain path as a server address, use the uexec connector with the
default freemountd and the path argument as the root directory.  It even
works with non-directory files.
freemount-client:  Use "." as the default address

This is perfect for fls and works just fine for fping (which is the only
one that worked at all with uloop even partially).
Merge branch 'exec'
freemount-client:  Reject an empty address early
f{ls,dir,stat}:  Work even if argc <= 1 (uses ".")