In rare cases of strings specifying true values near sys.maxint,
and oddball bases (not decimal or a power of 2), int(string, base)
could deliver insane answers.  This repairs all such problems, and
also speeds string->int significantly.  On my box, here are %
speedups for decimal strings of various lengths:

length speedup
------ -------
 1       12.4%
 2       15.7%
 3       20.6%
 4       28.1%
 5       33.2%
 6       37.5%
 7       41.9%
 8       46.3%
 9       51.2%
10       19.5%
11       19.9%
12       23.9%
13       23.7%
14       23.3%
15       24.9%
16       25.3%
17       28.3%
18       27.9%
19       35.7%

Note that the difference between 9 and 10 is the difference between
short and long Python ints on a 32-bit box.  The patch doesn't
actually do anything to speed conversion to long:  the speedup is
due to detecting "unsigned long" overflow more quickly.

This is a bugfix candidate, but it's a non-trivial patch and it
would be painful to separate the "bug fix" from the "speed up" parts.