Correction to PET 'Cosine' method

Small bug was fixed.
Minor correction to PET Cosine method

Minor correction to neglect negative PET values produced by Cosine
method.
Updates to Cosine method for PET

minor correction to Cosine method for PET.
Bug in fastscape_sp

Charlie reported a bug where fastscape_stream_power complained if
neither timestep nor rainfall_intensity was specified; should now be
resolved.

Also implemented a quick and dirty fix that should resolve the
PC-specific problem with the scipy.weaves where an error is printed
every timestep.
added couple of property functions to raster.py

1. added properties: number_of_cell_columns and number_of_cell_rows to
raster.py
2. boundary_cell_count function from sgrid is a valid function. Added
anti-deprecation request.
updates to grid/hex.py and hex_lattice_tectonicizer.py
Merge branch 'master' of https://github.com/landlab/landlab
Adding functionality to generate_uniform_precip

Added two new methods to generate_uniform_precip,
yield_storm_interstorm_duration_intensity() and elapsed_time
(property). The former enables a generator interface so you can do
calls like

>>> for (interval, rain_rate) in yield_storm…intensity():
>>>    #the code

As if we don’t need to save the storm sequence, this will be a lot
faster. The iterator is smart enough to terminate and truncate the
final step according to the run_time.

The property method then provides a way for a driver using the
generator to get at the total time elapsed.
New driver for storm driven stream power

I’m playing around with using the Jordan’s storm generator to drive a
stream power model. This “works” as-is, but is pretty unstable.
tweak driver and params for storm driven SP

minor tweaks to driver etc
stream_power no longer flattens nodes

It is now forbidden for the stream_power module to completely flatten
the gradient along its flow path. It now dramatically reduces it, but
leaves 10**-6 of the incision to preserve the flow structure.

This can be reversed once we have ponding working.
mainly saved datafiles; script to make AGU plot

An assortment of saved datafiles etc supporting AGU work. I realise
this should be in a more sensible place; I’ll move it ASAP.
Merge branch 'master' into sed-flux-dep

Conflicts:
	landlab/components/stream_power/fastscape_stream_power.py