BF: For complex signals, return both the negative and positive spectrum

And frequencies.
Merge pull request #115 from arokem/negative_freqs

BF: For complex signals, return both the negative and positive spectrum
first fix to py3k branch for tests to pass
fix test_TimeArray_div test
dict.items is an iterator in py3k
fix map craziness in py3k
fix zip shenanigans in py3k
fix more map craziness
np.array doesn't know what to do with zip in py3k
reload triggers different errors on py3k
fix in-place division in py3k
autocoversion for py3k thanks to python-modernize

The specific branch of python-modernize we use is here:
https://github.com/mitsuhiko/python-modernize/pull/5

5e95f82684adf0d679116fbdabeeb46649f0b970
no execfile in py3k
add PPAs to get TravisCI going with python3

trying Thomas' python3 PPA
add six dependency
add networkx dependency
Handle variations between different minor versions of py3k.
Merge branch 'py3k' of https://github.com/ivanov/nitime into pi=py3k
TST : deal with failing doctests.
More handling of failing tests.