pd.Timedelta constructor should accept nanoseconds attribute in the arguments
xref #9226 

Noticing an inconsistency. pd.Timedelta doesn't allow nanoseconds in constructor but its components list till nanoseconds. Here is what I can reproduce. (used then current master on OS X 10.10.1)

Example:

<pre>
Python 2.7.9 (v2.7.9:648dcafa7e5f, Dec 10 2014, 10:10:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from pandas.tslib import Timedelta
>>> td = Timedelta(nanoseconds=1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pandas/tslib.pyx", line 1723, in pandas.tslib.Timedelta.__new__ (pandas/tslib.c:29743)
raise ValueError("cannot construct a TimeDelta from the passed arguments, allowed keywords 
are " [days, seconds, microseconds, milliseconds, minutes, hours, weeks]
>>> td=Timedelta(seconds=1)
>>> td.components._fields
('days', 'hours', 'minutes', 'seconds', 'milliseconds', 'microseconds', 'nanoseconds')
</pre>
