Improve wheel support in pex.

pex/http.py

@@ -7,6 +7,7 @@
 import shutil
 import uuid
 from abc import abstractmethod
+
 from email import message_from_string
 
 from .common import safe_mkdtemp, safe_open

pex/pex_builder.py

@@ -9,7 +9,6 @@
 import tempfile
 
 from pkg_resources import DefaultProvider, ZipProvider, get_provider
-from wheel.install import WheelFile
 
 from .common import Chroot, chmod_plus_x, open_zip, safe_mkdir, safe_mkdtemp
 from .compatibility import to_bytes
@@ -274,6 +273,7 @@ def _add_dist_zip(self, path, dist_name):
     # But wheels don't have to be importable, so we need to force them
     # into an importable shape. We can do that by installing it into its own
     # wheel dir.
+    from wheel.install import WheelFile
     if dist_name.endswith("whl"):
       try:
         tmp = tempfile.mkdtemp()

setup.py

@@ -61,6 +61,7 @@
     'twitter.common.lang>=0.3.1,<0.4.0',
     'twitter.common.testing>=0.3.1,<0.4.0',
     'twitter.common.dirutil>=0.3.1,<0.4.0',
+    'wheel==0.29.0',
     'pytest',
   ],
   entry_points = {