BUG: Update plot when model_changed event is fired.

The scalar_image_function_inspector doesn't update the view when
model's function and other traits are changed.
Fix a bug which was causing axis objects to draw upside down.
Fix the position of a PlotAxis when it is not an overlay.
Add an origin trait to PlotAxis for component-free axes.
Fix marker_size indexing for ColormappedScatterPlot
Use itertools to avoid unnecessary array and list creation
Merge pull request #92 from enthought/bug/shell-marker-v

Fix typo in conversion for inverted-triangle marker.
Add Mac keys for history navigation to docstrings.
Merge pull request #93 from enthought/doc/zoom-history-keys

DOC: Fix docstring description of zoom-history keyboard shortcuts.
Make chaco_trait_editor demo qt compatible.
Remove wx.Timer dependency.
Save demo frame instance so that it isn't garbage collected.

Requires https://github.com/enthought/enable/pull/92.

This fixes a segfault which shows up when these examples are run
from a Qt-based IDE.
Fix example so that it runs in existing event loop.

This was a known issue (see FIXME comment that was deleted in this commit).
Remove wx-dependency from data_stream example.

Reuse generic Traits classes instead of requiring a wx app. This change was
thoroughly tested in ipython (with all permutations of wx/qt backends and
ETS_TOOLKITs). This was run in Mac and Windows version of the IDE, and
I checked demo.py with ETS_TOOLKIT set to wx and qt.
Save demo windows so they don't get garbage collected.
Fix bounds arguments to `img_plot`.
Updated _data_update_handler to react to "removed" and "added" events from PlotData class.  Removed deprecated .has_key() dictionary methods.
Workaround for agg issue.

Some agg functions don't play nice with numpy ints, so use a float
for the height. See enable issue #95.
Fix example docstring, add to demo application.
Correct typo, comment about deprecating class.