DataFrame.groupby bug
pandas latest commit: When groupby using multiple columns, I get a TypeError. Furthermore, the TypeError is different on 64bit and 32bit Linux machines.

In [1]: import pandas

In [2]: a = pandas.DataFrame(randn(2, 3))

In [3]: a
Out[3]: 
   0       1       2  
0 -0.7262  0.9849  0.1685
1 -1.0241 -2.3102 -1.1348

In [4]: g = a.groupby([0, 1])

In [5]: g.sum()
Out[5]: 
# on Ubuntu64 11.10; numpy 1.6.1

TypeError: object of type 'int' has no len()
# on sles10 32bit; numpy 1.5.1

TypeError: array cannot be safely cast to required type

---
# The following works fine on the 64bit machine, but not on the 32bit:

In [6]: a = pandas.DataFrame(randn(2, 3), columns=['a', 'b', 'c'])

In [7]: a
Out[7]: 
   a        b       c  
0  0.04682  0.1323  0.5046
1 -0.15613  0.4555  0.4553

In [8]: g = a.groupby(['a', 'b'])

In [9]: g.sum()
Out[9]: 
# on sles10 32bit; numpy 1.5.1

TypeError: array cannot be safely cast to required type

---

This bug was not present in the pypi version of pandas. However, that version has a Series index overflow bug on the 32bit machine:

In [10]: a = pandas.Series(randn(2))

In [11]: a
Out[11]: 
0     0.08557
1    -0.3659

In [12]: a[100]
Out[12]: 8.318223500663e-312
