use lsb_release to determine the codename
choose package archive based on lsb_release distributor
only copy MOZCONFIG if it's already set
just use the pre-existing $USER environment variable
redo how we get dependencies installed

build-dep for Iceweasel in Debian Wheezy appears to be busted.  mach
bootstrap installs individual packages instead of using build-dep and is
more likely to be correct.  Using mach bootstrap also means that we
avoid any differences between the source package names we need to use
(iceweasel on Debian, firefox on Ubuntu, etc.).
Merge pull request #1 from froydnj/build-debian

modify scripts so things build on debian, too