Timestamp constructor parses ISO 8601 incorrectly near DST boundaries
Original post, edited to correct ISO 8601 formats.  The originally titled bug does not exist.  There is, however, some unexpected behavior:

> It looks like short-form ISO 8601 parsing uses the right sign after all:
> 
> ``` python
> In [1]: import pandas as pd
> 
> In [2]: t = pd.Timestamp('2013-11-03 1:30:00', tz='America/Havana')
> 
> In [3]: t.strftime('%Y-%m-%d %H:%M:%S %Z %z')
> Out[3]: '2013-11-03 01:30:00 CST -0500'
> 
> In [4]: t.strftime('%Y%m%dT%H%M%S%z')   # ISO 8601 short format
> Out[4]: '20131103T013000-0500'
> 
> In [5]: pd.Timestamp(t.strftime('%Y%m%dT%H%M%S%z'))
> Out[5]: Timestamp('2013-11-03 01:30:00-0500', tz='tzoffset(None, -18000)')
> 
> In [6]: t == _
> Out[6]: True   # Not a bug after all!
> 
> In [7]: t.strftime('%Y-%m-%dT%H:%M:%S%z')   # ISO 8601 long format
> Out[7]: '2013-11-03T01:30:00-0500'
> 
> In [8]: pd.Timestamp(t.strftime('%Y-%m-%dT%H:%M:%S%z'))
> Out[8]: Timestamp('2013-11-03 01:30:00-0500', tz='pytz.FixedOffset(-300)')   # why pytz?
> 
> In [9]: t == _
> Out[9]: True
> 
> In [10]: t.strftime('%Y%m%dT%H%M%SZ%z')   # Not a real ISO 8601 format (note the 'Z')
> Out[10]: '20131103T013000Z-0500'
> 
> In [11]: pd.Timestamp(t.strftime('%Y%m%dT%H%M%SZ%z'))
> Out[11]: Timestamp('2013-11-03 01:30:00+0500', tz='tzoffset(None, 18000)')
> # This is the behavior that inspired the bug report.  I don't know if this is a valid parse
> # or not, but it sure is unexpected.
> ```
> 
> It would be awfully embarrassing if I filed a bug report because I couldn't read ISO 8601...

However, in the process of investigating this issue, I encountered the following, which is definitely a bug:

``` python
In [12]: ts = ['2013-11-%s3 %s1:30:00' % (x, y) for x in ['', '0'] for y in ['', '0']]

In [13]: ts
Out[13]: 
['2013-11-3 1:30:00',
 '2013-11-3 01:30:00',
 '2013-11-03 1:30:00',
 '2013-11-03 01:30:00']   # only this one is ISO 8601

In [14]: tzs = ['America/%s' % s for s in ['Chicago', 'New_York', 'Havana']]

In [15]: [[pd.Timestamp(t, tz=tz) for t in ts] for tz in tzs]
Out[15]: 
[[Timestamp('2013-11-03 01:30:00-0600', tz='America/Chicago'),
  Timestamp('2013-11-03 01:30:00-0600', tz='America/Chicago'),
  Timestamp('2013-11-03 01:30:00-0600', tz='America/Chicago'),
  Timestamp('2013-11-03 01:30:00-0500', tz='America/Chicago')],   # DST
 [Timestamp('2013-11-03 01:30:00-0500', tz='America/New_York'),
  Timestamp('2013-11-03 01:30:00-0500', tz='America/New_York'),
  Timestamp('2013-11-03 01:30:00-0500', tz='America/New_York'),
  Timestamp('2013-11-03 01:30:00-0400', tz='America/New_York')],   # DST
 [Timestamp('2013-11-03 01:30:00-0500', tz='America/Havana'),
  Timestamp('2013-11-03 01:30:00-0500', tz='America/Havana'),
  Timestamp('2013-11-03 01:30:00-0500', tz='America/Havana'),
  Timestamp('2013-11-03 00:30:00-0500', tz='America/Havana')]]   # Just plain wrong
```

I'm not sure what's going on here.
