ENH date_range accepts timedelta as freq
fixes #6307

Can you also update the date_range docstring?
 you need to fail this if u r on numpy < 1.7 (use pd._np_under_p17); raise that it is not supported (see pd.to_timedelta) for what to do

and skip tests if the same (np.timdelta64 has a diff signature under 1.6)
 whoops, I had made docstring, but forgot to save that file.

Thanks, will fix up for <1.7.
 looks like datetime timedelta don't have a total_seconds attribute in 2.6.
 yep see my comment in the pr - just pull out the days, seconds and microseconds directly 
 @hayd any thoughts about not having this always return micro/nano and instead a higher freq if possible?
 Yeah, will have another look at this tomorrow.

It begs question should we _always_ be simplifying ticks?

```
Second(30) + Second(30) == Second(6)  # not Minute(1)
```
 hmm offhand I'll say that the resample code doesn't care whether it's simplified or not (and doesn't make a difference) - 

can u give a look. see to see if it matters?
 resample won't _care_, will be in the freq repr for the index...

datetime.timedelta does some simplifying think we probably should. sigh, to micros being timedeltas smallest unit, this means the delta attribute does different things for nano and everything else:

In [21]: Nano(1000) == Micro(1)
Out[21]: False

Will fix as part of this...
 @hayd ok with merging this like this (after rebase)....then maybe create another issue about the simplification stuff?
 yea, I refactored this a little already (but not pushed and away atm) so future change should be straightforward. Will do next week.
 ping!
 ping
 moving to 0.15
 related #5963.
 I think the pending part of this was comparison of Tickers (previously `Nanos(1000) != Micro(1)`). Think this should be fixed...
 if u want to go down the rabbit hole
ok (1.6 is really broken though) but do after 0.14
 Note: docstring doesn't require changing as it already suggests that a timedelta should work.
 pls change release notes to v0.14.1 thanks!
 added and green (on my travis).
 I think it makes sense to simply if its unambiguous
 agree, done. Also removed some "horrible-ness".
 Hmmm I thought this had already been merged in.
 rebase this, and I think you have a 2.6 failing issue
 @hayd ?
 @hayd let's revist
 Sigh, it's only 2.6 that's at issue here (should probably remove the  `if not _np_version_under1p7` in tests...), I just need to install/build against 2.6 (ahem!)
 @hayd ?
 @hayd ?
 closing as stale. @hayd if you'd like to update, pls reopen
