Patch few bugs in distutils.ext.

This version seems able to install at list the empty package

distutils.ext/obidistutils/serenity/checkpython.py

@@ -11,6 +11,7 @@ import glob
 import re
 
 from obidistutils.serenity.checksystem import is_windows_system
+import sys
 
 
 def is_python_version(path=None,minversion='3.4',maxversion=None):
@@ -75,5 +76,63 @@ def lookfor_good_python(minversion='3.4',maxversion=None,followLink=False):
         
     return exe
 
-           
+def is_a_virtualenv_python(path=None):
+    '''
+    Check if the python is belonging a virtualenv
+    
+        @param path: the path pointing to the python executable.
+                     if path is None then the running python is
+                     considered.
+        @param path: str or None 
+                     
+        @return: True if the python belongs a virtualenv
+                 False otherwise
+        @rtype: bool
+                 
+    '''
+    if path is None:
+        rep = sys.base_exec_prefix == sys.exec_prefix
+    else:
+        command = """'%s' -c 'import sys; print(sys.base_exec_prefix == sys.exec_prefix)'""" % path
+        p = subprocess.Popen(command, 
+                             shell=True, 
+                             stdout=subprocess.PIPE)
+        rep = eval(str(p.communicate()[0],'utf8'))
+        
+    return rep
+
+
+def which_virtualenv(path=None,full=False):
+    '''
+    Returns the name of the virtualenv.
+        @param path: the path to a python binary or None
+                     if you want to consider the running python
+        @type path: str or None
+                     
+        @param full: if set to True, returns the absolute path,
+                     otherwise only return a simple directory name
+        @type full: bool
+                 
+        @return: the virtual environment name or None if the
+                 path does not belong a virtualenv
+        @rtype: str or None
+    '''
+    if path is None:
+        path = sys.executable
+    
+    if is_a_virtualenv_python(path):
+        parts = path.split(os.sep)
+        try:
+            if full:
+                rep = os.sep.join(parts[0:parts.index('bin')])
+                rep = os.path.realpath(rep)
+            else:
+                rep = parts[parts.index('bin')-1]
+        except ValueError:
+            rep = None
+    else:
+        rep=None
+        
+    return rep
+