[SyncEvolution] Detect python binary name in build time

Hello, there is some effort to rename 'python' to 'python2' in the distributions, but SyncEvolution still uses 'python' (without the version number) in its scripts. I made a change for Fedora to detect the installed python 2 binary name and use it in the scripts. I know, an ideal solution would be to port to python3 at the same time, but it's out of my knowledge, I do not speak pythonish and simple change to /usr/bin/python3 makes the provided scripts not to run with a runtime error about syntax and such, thus I decided to offer at least this change to you. Maybe I'll convince someone with python knowledge to port the scripts to python3, in which case I'd return back to you with a follow up change, if you are interested. Bye, Milan