[RFC] 09/10 Add "continue --all"

[Joel Brobecker]

> If you don't like the all prefix then we can go back to continue
> --all, or even just continue all.  Continue takes a numeric argument
> and all will not conflict.

FWIW, I like "continue all", but I think I prefer the "all" prefix.
I would probably have "all continue" be its own command rather
than having it an alias of "thread apply all continue" for the
reasons that Pedro mentioned, and it shouldn't be much more work than
the solution based on command aliasing.

Using the "all" command prefix would be very elegant when we add
more commands.  This assumes that there are other commands that
we'd like to provide under that same prefix.

-- 
Joel