contrib/scripts/install_prereq: Don't install 32-bit packages on 64-bit hosts

On Debian based systems, the install_prereq tool uses a search command on
Debian that results in selecting both 64-bit and 32-bit packages. Besides the
waste of disk space, this can actually cause aptitude use 100% of memory on a
VM with 1GB of RAM as it tried to work out all of the 32-bit package
dependencies.

This patch filters out the 32-bit packages on a 64-bit machine, and leaves
32-bit machines alone.

ASTERISK-24048 #close
Reported by: Ben Klang
Tested by: Ben Klang, Matt Jordan
patches:
  install_prereq_64-bit_compat.patch uploaded by Ben Klang (License 5876)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@430798 65c4cc65-6c06-0410-ace0-fbb531ad65f3