Fixed whitespace bug when pasting IPython continuation prompt.

Fixes a SyntaxError that arose when pasting code containing the IPython
continuation prompt without a trailing white space, such as:

In[1]: if True:
   ...:    print "No space after ':' on next line."
   ...:

This might arise if the user only copies up to the end of the last
prompt, without copying the trailing whitespace.

This commit adds a regression test and fixes the regular expression that
strips continuation prompts, making the whitespace optional.

IPython/core/inputtransformer.py

@@ -461,7 +461,7 b' def classic_prompt():'
 def ipy_prompt():
     """Strip IPython's In [1]:/...: prompts."""
     # FIXME: non-capturing version (?:...) usable?
-    prompt_re = re.compile(r'^(In \[\d+\]: |\s*\.{3,}: )')
+    prompt_re = re.compile(r'^(In \[\d+\]: |\s*\.{3,}: ?)')
     return _strip_prompts(prompt_re)
 
 

IPython/core/tests/test_inputtransformer.py

@@ -233,6 +233,11 b' syntax_ml = \\'
           ('...:     print i','    print i'),
           ('...: ', ''),
           ],
+         [('In [24]: for i in range(10):','for i in range(10):'),
+          # Space after last continuation prompt has been removed (issue #6674)
+          ('...:     print i','    print i'),
+          ('...:', ''),
+          ],
          [('In [2]: a="""','a="""'),
           ('   ...: 123"""','123"""'),
           ],