android: Introduce new "mirror fetcher" shell script

fetch.sh will try downloading our dependencies from several different
mirrors, in case the project's main website is down.  Add known-good SHA1
hashes to android/Makefile so fetch.sh can detect bad downloads.

This is intended to work in a similar manner to the OpenWRT downloader
(which unfortunately was too closely coupled with their build system to
reuse as-is).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Introduce $(FOO_TAR) variables for each dependency

This will make it easy to iterate through the entire list of tarballs.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Add "make mirror-test" target

This downloads each tarball from each mirror listed in fetch.sh and checks
the SHA1 hash.  It would be a good idea to run this after adding/changing
a package [version] or a mirror.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Update openssl to 1.0.1g

This eliminates the DTLS_BAD_VER patch and fixes Heartbleed.

(Obviously we default to GnuTLS for Android builds now, but the OpenSSL
build still passes basic smoke tests.)

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Update to GnuTLS 3.2.13

This drops permissive RFC2818 wildcards, like "f*.com", in favor of the
stricter RFC6125 guidelines.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>