Problem: python310 condition missing

Solution: implement and document it

doc/topics/variables-extending-and-substitutions.rst

@@ -202,6 +202,7 @@ python36       True if running Python 3.6
 python37       True if running Python 3.7
 python38       True if running Python 3.8
 python39       True if running Python 3.9
+python310      True if running Python 3.10
 sys_version    ``sys.version.lower()``
 pypy           True if running PyPy
 jython         True if running Jython

src/zc/buildout/buildout.py

@@ -1764,7 +1764,7 @@ def _default_globals():
 
     # minor python major_python_versions as python24, python25 ... python39
     minor_python_versions = ('24', '25', '26', '27',
-                             '30', '31', '32', '33', '34', '35', '36', '37', '38', '39')
+                             '30', '31', '32', '33', '34', '35', '36', '37', '38', '39', '310')
     for v in minor_python_versions:
         globals_defs['python' + v] = ''.join(major_python_versions[:2]) == v
 

src/zc/buildout/tests/configparser.test

@@ -291,7 +291,7 @@ called by buildout::
 
   # major and minor python versions, yes even python 3.5 and 3.6 are there , prospectively
   # comment: this expression "is true" and not that long expression cannot span several lines
-  [s2: any([python2, python3, python24 , python25 , python26 , python27 , python30 , python31 , python32 , python33 , python34 , python35 , python36, python37, python38,python39]) ]
+  [s2: any([python2, python3, python24 , python25 , python26 , python27 , python30 , python31 , python32 , python33 , python34 , python35 , python36, python37, python38, python39, python310]) ]
   b = 1
 
   # common python interpreter types