Make sure to pass all variables defining the proper python version as found by
robotpkg, otherwise ros CMakeFiles may happily find python-3.2 and use it
instead of python<3, although this does not work in the end (at least ros-rx
does this and breaks on F17).

This is done in the common ros Makefile as this affects all packages.

Some ros python packages require py-setuptools instead of using vanilla
distutils. This has the side effect of installing so called EGG_INFO
directories that behave differently depending on the platform (sometimes the
directory is zipped, sometimes not). The PLIST may then be broken.

Instead of fighting with this, just use distutils instead of setuptools since
setuptools does not bring anything useful in robotpkg (does it?). This is done
via a SUBST stage in setup.py for packages that declare using it.

Affected packages are, so far:
 - ros-gencpp
 - ros-genlisp
 - ros-genpy

Factor out the following:
 - PKGNAME with ros- prefix. This is overrided for a few base pkgs only
 - MAINTAINER
 - LICENSE

These can still be overriden on a per pkg basis.

C++ code generator for ROS .msg and .srv files

Project genmsg exists in order to decouple code generation from ROS .msg & .srv
format files from the parsing of these files and from impementation details of
the build system (project directory layout, existence or nonexistence of
utilities like rospack, values of environment variables such as
ROS_PACKAGE_PATH): i.e. none of these are required to be set in any particular
way.