Move logic that determines if item can be directly composited into separate per-item #_canComposite() method.
Fix namespace for images in SVGExport.
Fix project.clear() so it removes all layers properly.
Merge pull request #241 from chrisbarmonde/master

Fix project.clear()
Define failing test for #246
Fix tests for #246.

This is actually the right behavior: Setting length to negative values should flip around defined vectors.
Merge branch 'master' of github.com:paperjs/paper.js
Implement failing test for #243.
Improve new hit-testing test.
Take #visible state into account when hit-testing.

Closes #243.
Implement failing test for hit-testing guides.
Improve hit-testing tests for guides.
Fix hit-testing for guides.
Clean up Item#hitTest() code.
Define failing test for hit-testing bounds on raster items.

Linked to issue #247.
Use local bounds for hit-testing.

Fixes issue #247.
Bring back _class names, since code minification breaks reliance on constructor.name.

Closes #248.
Improve prepro.js' stripComments() method to respect regular expressions.
Prevent overriding exported classes by inheriting classes with same _class value.
Move PaperScript.get/setAttribute() to PaperScope.