windows: add doctest for shellquote()

This is actual test coverage for issue4629.  The test changes in eea3977e6fca
were simply the addition of quotes to the output, not ensuring that strings with
backslashes are quoted.

mercurial/windows.py

@@ -162,6 +162,18 b' def samestat(s1, s2):'
 _quotere = None
 _needsshellquote = None
 def shellquote(s):
+    r"""
+    >>> shellquote(r'C:\Users\xyz')
+    '"C:\\Users\\xyz"'
+    >>> shellquote(r'C:\Users\xyz/mixed')
+    '"C:\\Users\\xyz/mixed"'
+    >>> # Would be safe not to quote too, since it is all double backslashes
+    >>> shellquote(r'C:\\Users\\xyz')
+    '"C:\\\\Users\\\\xyz"'
+    >>> # But this must be quoted
+    >>> shellquote(r'C:\\Users\\xyz/abc')
+    '"C:\\\\Users\\\\xyz/abc"'
+    """
     global _quotere
     if _quotere is None:
         _quotere = re.compile(r'(\\*)("|\\$)')