BUG: pd.Timedelta does not accept np.int32, etc.
pd.Timedelta is a great addition, thanks! 

Is it the intended behavior of pd.Timedelta to only accept np.int64, python ints, and python floats? I ran into this when I tried to construct a list of pd.Timedeltas from the np.int32 array returned by pd.DatetimeIndex.dayofyear. 

``` python
>>> import pandas as pd
>>> import numpy as np
>>> pd.Timedelta(days=np.int64(1))
Timedelta('1 days 00:00:00')
>>> pd.Timedelta(days=np.int32(1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/tslib.pyx", line 1638, in pandas.tslib.Timedelta.__new__ (pandas/tslib.c:27693)
ValueError: cannot construct a TimeDelta from the passed arguments, allowed keywords are [days, seconds, microseconds, milliseconds, minutes, hours, weeks]
>>> pd.Timedelta(days=np.int16(1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/tslib.pyx", line 1638, in pandas.tslib.Timedelta.__new__ (pandas/tslib.c:27693)
ValueError: cannot construct a TimeDelta from the passed arguments, allowed keywords are [days, seconds, microseconds, milliseconds, minutes, hours, weeks]
>>> pd.Timedelta(days=np.float64(1))
Timedelta('1 days 00:00:00')
>>> pd.Timedelta(days=np.float32(1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/tslib.pyx", line 1638, in pandas.tslib.Timedelta.__new__ (pandas/tslib.c:27693)
ValueError: cannot construct a TimeDelta from the passed arguments, allowed keywords are [days, seconds, microseconds, milliseconds, minutes, hours, weeks]
>>> pd.Timedelta(days=1)
Timedelta('1 days 00:00:00')
>>> pd.Timedelta(days=1.0)
Timedelta('1 days 00:00:00')
```

Here's my version info:

``` python
>>> pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-431.17.1.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.15.1
nose: 1.3.4
Cython: 0.21
numpy: 1.9.1
scipy: 0.14.0
statsmodels: None
IPython: 2.3.0
sphinx: 1.2.3
patsy: None
dateutil: 2.2
pytz: 2014.9
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.4.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: 0.9.7
pymysql: 0.6.2.None
psycopg2: None
```
