Message 277413 - Python tracker

Simple implementation idea:

* add a pkg_config option to Extension()
* run subprocess.call(["pkg-config", self.pkg_config, "--exists"])
* if return value is 0, extend self.extra_compile_args with ["pkg-config", self.pkg_config, "--cflags"] and self.extra_link_args with ["pkg-config", self.pkg_config, "--libs"]
* otherwise print a warning

We could split and parse the output to handle -I, -L and -l in a more elegant way.