[gentoo-dev] autoconf now supports multislots

[Mike Frysinger]

for people who work with projects that require specific versions of autoconf 
and nothing else (like ==2.64), i've long left older versions in the tree so 
people could downgrade on the fly.  this isn't so bad as you can do:
	emerge -bk ~autoconf-2.64
	<use it>
	emerge -bk autoconf

but i'm super lazy, so even this manual step is annoying.  as such, i've added 
USE=multislot support to autoconf (just like it is with binutils & gcc).

now you can install multiple versions in parallel and run:
	WANT_AUTOCONF=2.64 autoconf
or more specifically:
	autoconf-2.64
without affecting the default `autoconf`.

the default is, of course, unchanged.
-mike