FIX run() should use the same python as the install/etc.
(cherry picked from commit 3cd981e91fca49aa13bae30d8c3e4470e20a0388)
ENH: warn against using --prefix (in main, not from EggInst class).
BUG: fix warning message when using 'egginst --prefix'.
Merge pull request #156 from enthought/workaround_egginst_scripts

Workaround egginst scripts