History length control added to PlotGroupPanel. The parameter maximum_plot_history_length now controls what is saved in history list as follows:
        If the parameter maximum_plot_history_length is -1, history aving s unlimited
        (except by your machine memory!!). If it is 0, then no history is saved. If
        it is N, then up to N plots are saved in history list.
Fixed issue with matrixplot opening a second bogus figure window in some circumstances; closes #504. Added matrixplot3dx3 command
Merge branch 'master' of github.com:ioam/topographica
Merge pull request #505 from mjabri/master

Plot history length control; defaults to keeping 20 plots instead of all plots, to avoid filling up memory.
Lancet support for Topographica now in topo/misc/launch.py
Renamed topo/misc/launch.py to topo/misc/tlancet.py
Fix for unnecessary OpenMP warnings in misc/commandline.py

Printed warning regarding use of the -g flag before OpenMP settings
(openmp_threads, openmp_min_threads, openmp_max_threads) was not being
generated correctly.
Fixed bug in decode_feature from 2007: was ignoring all but one of any activity value for a given feature value.  Not previously detected because each feature value was distinct for orientation and face preference maps, but for position maps there appear to be multiple with the same feature values but different activity values.
Merge branch 'master' of github.com:ioam/topographica
fixed errors in paramtk/odict.py doctests
attempt 2 at fixing paramtk/odict.py doctest errors
update lancet reference
remove non-nosified unit tests
move basepath code from topographica script to topo/__init__.py
fixed nose- and doctest-related errors
excluded functional tests from nose runner
tweaked topo.misc.unitsupport for passing nosetests
adjusted gui_tests.py for running with nose
remove unit target from old runner
remove coverage from old test runner