Added ImageExporter error message for zero-size export
Ordereddict exploses with python2.6 ...
Use the official backport
Workaround for OrderedDict bug: import from 'ordereddict' backport module if available
Add backport ordereddict to repository
Merge remote-tracking branch 'kif/master' into develop

Conflicts:
	pyqtgraph/pgcollections.py
Fixed improper tick spacing and axis scaling
This requires an API change:
 - AxisItem.setScale(float) has the usual behavior
 - AxisItem.setScale(None) is no longer allowed. Instead use:
 - AxisItem.enableAutoSIPrefix(bool) to enable/disable SI prefix scaling
Also makes the API more intuitive since these features are now accessed and implemented independently.
Updated documentation to match previous API change
Allow AxisItem.setScale(None) to retain API backward compatibility.
minor fix
Merge branch 'axis_fix' into develop
    Fixed improper tick spacing and axis scaling
    This requires an API change:
     - AxisItem.setScale(float) has the usual behavior
     - AxisItem.setScale(None) is deprecated (but still works). Instead use:
     - AxisItem.enableAutoSIPrefix(bool) to enable/disable SI prefix scaling
    Also makes the API more intuitive since these features are now accessed and implemented independently.

fixes #4
Merge remote-tracking branch 'upstream/develop' into develop
Use Luke's fix of bug #4