pd.Timedelta constructor should accept nanoseconds attribute in the arguments

[tvyomkesh]

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:

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 "", line 1, in 
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')

[jreback]

This is ONLY for an actual passed argument of 'nanoseconds'. String parsing/interp is good.

In [3]: pd.Timedelta('1ns').components
Out[3]: Components(days=0, hours=0, minutes=0, seconds=0, milliseconds=0, microseconds=0, nanoseconds=1)

[tvyomkesh]

@jreback I have changed the title accordingly. Timdelta constructor fails to accept when nanoseconds is supplied as an attribute but otherwise pd.Timedelta does support nanoseconds. Also default resolution in the constructor is nanoseconds. For e.g.,

In [7]: t4 = Timedelta(100)
In [8]: t4.components
Out[8]: Components(days=0, hours=0, minutes=0, seconds=0, milliseconds=0, microseconds=0, nanoseconds=100)

[tvyomkesh]

I am testing a fix for this. will submit a PR

[tvyomkesh]

Moved DateOffset nano related issue to a separate one here #9284 as it seems like a separate issue and not related to this one.