Give access to current profile path and base path in section

Solves bug described at https://bugs.launchpad.net/zc.buildout/+bug/767190.

Basically: Add a mechanism making possible to have two parameters (here, ${:_profile_base_location_} and ${:_profile_location_}) in section, which would expand to basename and location of current Buildout profile.

We don't have actual use of ${:_profile_location_}, do you think it can still be useful, or do I just get rid of it?


Finally trying to share and push what we are using in SlapOS for a while. This code is really helpful for us, could it be useful for all Buildout community as well?

You can find examples of such usage here : http://git.erp5.org/gitweb/slapos.git/blob/HEAD:/component/bison/buildout.cfg?js=1#l9