WIP: new attempt at dtopotools.py module and class organization
major changes to dtopotools2.py:
moved okada into SubFault class, added DTopography.read for topo_type 1, many bug fixes and improvements
debugging dtopotools2: added missing _strike_slip, _dip_slip, and set default mu value
need to flipud Y and dz when reading topo_type==1. Also fixed plot to use X,Y rather than x,y
added comments
Started adding defaults parameter to dtopotools.Fault.read -- need to rethink use of list for some parameters.
set env in run_tests.py
Merge branch 'master' into dtopotools2 after 5.2.0 release

* master: (27 commits)
  Merged changes to topotools.py from PR#87 into other recent changes to this file. Plan to close that PR.
  cleaned up plotting tests, fix axes
  use mirrors in pip install, following clawpack/.travis.yml
  change tests so nosetests can be run from top level directory
  cd to geoclaw/tests in travis: will all our tests be here?
  debugging travis with nosetests -s
  retest fetching url and remove test of plotting until clawpack/clawpack is updated so travis gets recent changes to visclaw (need add_colormaps)
  use Agg matplotlib backend for tests
  trying pip install matplotlib in .travis.yml
  test travis for plotting by adding apt-get install python-matplotlib to .travis.yml
  Travis fails for fetch_topo_url example so remove 'test' from the name of this test
  Changed tests to get Travis to work(?)... Take out plot tests and add main program to run these outside of nose. Print directory and files to try to debug kahului file not found.
  Moved and renamed tests/test_topotools.py (and data file).  Need to see if Travis works ok.
  Do not set .z attribute of Topograophy class unless its an unstructured grid
  Fixed new unit test for fetch_topo_url to delete metadata file
  Fixed Topography.read when argument is a URL, deprecated get_topo function and added improved version fetch_topo_url that is now used by read.  Added a unit test.
  fixed docstring in test_plot_kahului
  Some fixes to topotools.py, adjusted plotting so pcolor and imshow pixels are centered on x,y of topo, added test data and plotting of Kahului Harbor
  Improved test_new_topotools.py by adding assertions and test of crop function
  Fixed (?) Topography to set .X and .Y based on .x and .y if available.  Added test of cropping with plot.
  ...
dtopotools2.py: changed dimensions and coordinates to 4 attribures length,width,longitude,latitude
dtopotools2: changed topo_type to dtopo_type
added support for writing only 1 time for static dtopo file, added 'noaa sift' and 'bottom center' options for subfaults
working on time-dependent ruptures
added DTopography.animate_dz_colors for time dependent ruptures
Refactored SubFault.okada by separating out set_geometry function and cleaning up code.  Geometry of corners is also set for use in plotting.
added Fault.plot_subfaults adapted from old dtopotools.  Could be improved to add to existing plot more nicely.
Added Fault.plot_subfaults_depth
Added dtopotools2.strike_direction
moved 5.2.0 version of dtopotools.py to dtopotools_5_2_0.py: keep around for a while for backward compatibility
moved dtopotools2.py to dtopotools.py since this now has sufficient functionality.
changed SubFault.geometry to @property so set_geometry is only called once when needed