This slightly changes IsAvailableCommand in that a non-runnable command
with a runnable subcommand is now 'Available'
We also use IsAvailableCommand in the rest of the codebase instead of
half kinda sorta doing it incorrectly other places.
We previously had this weak argument called projectName which let you
set a single part of a man page header. Instead do the best we can if
the caller doesn't pass us anything, but let the caller specify anything
they want.
Eric Paris