autogen.sh update

[graydon h. <gr...@re...>]

hi,

talked to phil some more on IRC and came to a bit of a compromise for
autogen.sh, which is simply to require 3 smaller changes to it:

(1) reject automake 1.4 when someone tries to use it
(2) allow users to override specific binary names with env variables
(3) abort if anything fails to run

here is the patch.

-graydon