Fix issue 5230 by having pydoc's safeimport check to see if the import

error was thrown from itself in order to decide if the module can't be
found.  Thanks to Lucas Prado Melo for collaborating on the fix and tests.

Lib/pydoc.py

@@ -55,6 +55,7 @@ Richard Chamberlain, for the first implementation of textdoc.
 import sys, imp, os, re, types, inspect, __builtin__, pkgutil
 from repr import Repr
 from string import expandtabs, find, join, lower, split, strip, rfind, rstrip
+from traceback import extract_tb
 try:
     from collections import deque
 except ImportError:
@@ -299,9 +300,9 @@ def safeimport(path, forceload=0, cache={}):
         elif exc is SyntaxError:
             # A SyntaxError occurred before we could execute the module.
             raise ErrorDuringImport(value.filename, info)
-        elif exc is ImportError and \
-             split(lower(str(value)))[:2] == ['no', 'module']:
-            # The module was not found.
+        elif exc is ImportError and extract_tb(tb)[-1][2]=='safeimport':
+            # The import error occurred directly in this function,
+            # which means there is no such module in the path.
             return None
         else:
             # Some other error occurred during the importing process.