[Rock-dev] castxml support merged on master

[Sylvain Joyeux]

I've merged all the parts needed to use castxml instead of gccxml
(needed for ubuntu 15.10 and later). This is supported only for 15.04
and later because castxml does is supported only on clang >= 3.6.

Once you've updated, you can switch to castxml by adding

    Autoproj.env_set 'TYPELIB_CXX_LOADER', 'castxml'

to either your installation's autoproj/init.rb, or globally in
$HOME/.autoprojrc.
Once you switched, you will have to run an update & build to install castxml

Unless there are big showstoppers, the castxml importer will replace
in fine Typelib's own clang importer, to reduce maintenance load.

Sylvain