gpython: Include gevent version into banner
Gevent is major component gpython builds on - it deserves to be included into version and is handy to know if one hits a bug with gpython - to see in which particular runtime environment the bug was hit.
Before:
$ gpython
Python 3.7.3 (default, Dec 20 2019, 18:57:59)
[GCC 8.3.0] [GPython 0.0.6.post2] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>After:
$ gpython
Python 3.7.3 (default, Dec 20 2019, 18:57:59)
[GCC 8.3.0] [GPython 0.0.6.post2] [gevent 20.5.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>