python-utils-r1.eclass: Block also pythonX.Y in wrappers

python-utils-r1.eclass: Block also pythonX.Y in wrappers

Improve the wrapper blocking logic to block specific Python versions
as well rather than just 2/3.  In other words, for eselected pythonX.Y
both pythonZ (Z = X^1) and python*.* (!= X.Y) will be blocked.
Hopefully this will catch more build systems that hardcode Python
versions rather than respecting what we're giving them.

This will work only for build systems respecting PATH.  Build systems
(and ebuilds) using /usr/bin path directly will still be able to use
other Python versions.