Using this trick, the dependency in hrp2 is removed from the
jrl-walkgen.pc file.

This will avoid path issues with hrp2 ressources

The compilation and link informations should now be gathered in a .pc file

This reverts commit 7a49aa1b.

When checking, please be careful to have your wireless connection off.
It might jam the time profile.

O2 with -DNDEBUG is faster than O3 and previous flags
on a Xeon 3.2 GHz with 2Mb of L2 cache.

The flags needs further investigation.

More specifically take into account the new headers of
abstract-robot-dynamics.