Fix traceback in install_wheel() when --always-copy used

The embedded python script in this function imports tempfile, which in
turn needs to import _io.so. The munged pythonpath used for this script
does not contain this directory, causing the embedded script to fail to
import tempfile.

This commit resolves that traceback by adding the lib-dynload dirs from
sys.path to the munged pythonpath.

virtualenv.py

@@ -837,7 +837,8 @@ def install_wheel(project_names, py_executable, search_dirs=None,
         search_dirs = file_search_dirs()
 
     wheels = find_wheels(['setuptools', 'pip'], search_dirs)
-    pythonpath = os.pathsep.join(wheels)
+    dynload_dirs = [d for d in sys.path if d.endswith('/lib-dynload')]
+    pythonpath = os.pathsep.join(wheels + dynload_dirs)
 
     # PIP_FIND_LINKS uses space as the path separator and thus cannot have paths
     # with spaces in them. Convert any of those to local file:// URL form.