How to override which autoconf is used?

[David Holmes]

My build machine has autoconf 2.68 in /usr/bin but others use 2.67. This 
means we keep getting differences in generated-configure.sh that are not 
related to actual changes.

So I put the 2.67 version of autoconf first in my path:

  > which autoconf
/home/dholmes/bin/autoconf
  > autoconf -V
autoconf (GNU Autoconf) 2.67

but when I run autogen.sh (which simply calls "autoconf") the resulting 
file has:

#! /bin/sh
# Guess values for system-dependent variables and create Makefiles.
# Generated by GNU Autoconf 2.68 for OpenJDK jdk8.

???

How can I use 2.67 without having to actually downgrade it on a shared 
build machine ? :(

I've even tried copying autom4te to ~/bin and hacking the scripts 
directly. But I still get autoconf 2.68 ??? Makes no sense.

Thanks,
David