| Implemented Issue 21; added a new Property Constant (since the old one was incorrect) and deprecated the old one | 
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| core/src/main/java/edu/umd/cs/piccolo/PCanvas.java | 
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| core/src/main/java/edu/umd/cs/piccolo/PRoot.java | 
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| core/src/test/java/edu/umd/cs/piccolo/PCanvasTest.java | 
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