Clean up scripted builds

This patch set is intended to address a couple of items:

* F-Droid and others having trouble building native binaries from source (bug #208, bug #66, bug #180, bug #181)
* Fix "ant" builds from the command line (bug #65)
* Implement a more robust scheme for updating binaries and preferences after an AFWall upgrade (bug #204)
* Allow ICS+ users to fall back to the builtin iptables binaries, if their system binaries are unusable (bug #210)
* Remove hardcoded paths from the busybox builds, and eliminate the timestamp so that the output binary is (hopefully) deterministic
* README updates for build info and general readability
* Update to the latest iptables release, and split the Android deltas into discrete patches so it's easy to take new updates.  The new binaries have been lightly tested on JB 4.2.2 and GB 2.3.7.
* Add builtin ip6tables binaries; lightly tested on JB 4.2.2
* Add x86 and MIPS binaries; these still need to be tested

Side note: it looks like this project may have been registered at travis-ci.org a long time ago, but that is no longer the case.  Is it worth restarting these builds?