This patch adds a `struct inferior' object, and the code needed to
maintain an inferior list.  The patch adds an inferior.c file (looks
like it was just waiting for this) -- you'll notice that the code
is very similar in principle to gdbthread.h/thread.c.  That's not
a coincidence, this code was heavilly borrowed from there.

The object is still mostly empty in this patch.  The following
patches will start moving a couple of globals into it.

-- 
Pedro Alves