Expand the sys.path with entries from PYTHONEXTRAPATH

   This commit is part of fixup the "Add setup-eggs option in zc.recipe.egg:develop."

src/zc/buildout/buildout.py

@@ -1276,6 +1276,7 @@ class Buildout(DictMixin):
                 setuptools=zc.buildout.easy_install.setuptools_pythonpath,
                 setupdir=os.path.dirname(setup),
                 setup=setup,
+                path_list=[],
                 __file__ = setup,
                 )).encode())
             args = [sys.executable, tsetup] + args

src/zc/buildout/easy_install.py

@@ -1148,10 +1148,16 @@ def develop(setup, dest,
         undo.append(lambda: os.remove(tsetup))
         undo.append(lambda: os.close(fd))
 
+        extra_path = os.environ.get('PYTHONEXTRAPATH')
+        extra_path_list = []
+        if extra_path:
+          extra_path_list = extra_path.split(os.pathsep)
+
         os.write(fd, (runsetup_template % dict(
             setuptools=setuptools_pythonpath,
             setupdir=directory,
             setup=setup,
+            path_list=extra_path_list,
             __file__ = setup,
             )).encode())
 
@@ -1579,6 +1585,10 @@ runsetup_template = """
 import sys
 sys.path[:0] = %(setuptools)r, %(setupdir)r
 
+for extra_path in %(path_list)r:
+  sys.path.insert(0, extra_path)
+
+
 import os, setuptools
 
 __file__ = %(__file__)r