Merge pull request #3338 from takluyver/i3316

closes  #3316

According to [documentation here](http://docs.activestate.com/activepython/2.4/pywin32/win32api__SearchPath_meth.html),
SearchPath takes an optional third parameter for the extension,
which is only added if the filename doesn't have an extension.

IPython/utils/_process_win32.py

@@ -82,7 +82,7 b' def _find_cmd(cmd):'
         path = None
         for ext in extensions:
             try:
-                path = SearchPath(PATH, cmd + ext)[0]
+                path = SearchPath(PATH, cmd, ext)[0]
             except:
                 pass
         if path is None: