Introduce TERMUX_PKG_INCLUDE_IN_DEVPACKAGE as a method of
specifying additional files for -dev packages, and use that to
add bin/xml2-config (which is needed to e.g. install the python
lxml package) to libxml2-dev.
Should fix https://github.com/termux/termux-app/issues/8
Also change subpackage containing xmllint to libxml2-utils to
match debian.
This fixes Android 6 problems (so closes#26).
It also rebuilds termux-elf-cleaner when needed
and bumps some build revisions for packages
needed updates to remove DT_VERDEF and DT_VERDEFNUM.
