properly reference ".pexrc" as relative to the pex file itself.

pex/variables.py

@@ -5,6 +5,7 @@
 # checkstyle: noqa
 
 import os
+import sys
 from contextlib import contextmanager
 
 from .common import die
@@ -47,15 +48,14 @@ def set(self, variable, value):
 
   def _from_rc(self, rc):
     ret_vars = {}
-    for filename in [rc, '.pexrc']:
+    for filename in [rc, os.path.join(os.path.dirname(sys.argv[0]), '.pexrc')]:
       try:
         with open(os.path.expanduser(filename)) as fh:
           ret_vars.update(dict(map(lambda x: x.strip().split('='), fh)))
       except IOError:
         continue
     return ret_vars
 
-
   def _get_bool(self, variable, default=False):
     value = self._environ.get(variable)
     if value is not None: