Check that the path is not empty before calling CGContextClosePath or CGContextClip
Fix test of points-to-pixel conversion.

The conversion factors for points to pixels has been 1 for a very long time,
but the test assumed something other factor.
Fix the testURLFallback test failure.
Merge pull request #69 from WarrenWeckesser/quartz-empty-path

Quartz backend: Don't call CGContextClosePath or CGContextClip with an empty path
Merge pull request #86 from enthought/test/fix-unit-conversion-test

Fix test of points-to-pixel conversion.
Be more specific about the exception type from parsing a brush URL
Merge remote-tracking branch 'origin/test/fix-unit-conversion-test' into test/fix-svg-url-fallback
Merge pull request #87 from enthought/test/fix-svg-url-fallback

Fix the testURLFallback test failure.
REL: Update version for 4.3.0 release.
Image backend now properly passes along alpha channel.
Merge pull request #102 from brett-patterson/master

Transparency bug with image backend
Copy LayoutBox from Enaml.
Add a ConstraintsContainer which doesn't do much yet.
Construct a simple demo for testing constraints layout.
Add the LayoutManager class from Enaml.
Add a little more to the ConstraintsContainer.
Start adding constraints to Component.
Fix a typo.
Add fixed constraints management.
Tie up some loose ends.