DOC: Note journal impact for papers that use PyMVPA as a method

Also note the cummulative impact for 2009-2012 (fresher stats aren't
available yet).
ENH: no need to double safe-guard imports of GLMMappers + exclude GLMMapper from 'import *'

This should also make 'make testsuite' happy while allowing for less code, and not
changing 'API' for anyone who did 'from mvpa2.suite import *' before ;)