Message 267796 - Python tracker

To avoid bloating pyshell.main further, and to facilitate testing, I put the new code in a separate function called from main and a test.  The test should PASS as is and FAIL on X11 with the call to fix_x11_paste commented out.  If it does not, it is not a test and should be modified. When we have a real test, I will apply.  x11-paste.diff is against 3.6.  I already have 2.7 and 3.5 versions.