python.spec needs to create python2.exe and python3.exe

[dmik]

Currently, only symlinks are installed for those, but they are not usable outside LIBC (e.g. in plain REXX/CMD scripts or in the CMD command prompt).

We have EXEs (in addition to symlinks) for python2.7 and python 3.x, so we should have them for major versions as well.

[dmik]

Another related issue is that it's not easy to install python-unversioned-command (to have the recent python3 as python.exe) because it conflicts with python2.7-unversioned-command but that one is impossible to remove due to numerous dependencies (including yum itself). It can be replaced via yum shell but it's not obvious for a regular user.