Add accumulate argument to PathAnimationEffect constructor

This allows the accumulation attribute of a PathAnimationEffect to be set,
which previously was not possible.

Note that the patch [1] to fix this in the spec narrowly missed FPWD.

[1] https://dvcs.w3.org/hg/FXTF/rev/f55c175711df
Merge pull request #296 from steveblock/passAccumulateToPathAnimationEffect

Add accumulate argument to PathAnimationEffect constructor
Allowed animations to work with null target.
Added test for animations with null targets.
Added null target test 'test-null-target.html' to testcases.js.
Fix a bad rebase in normalizeKeyframeDictionary()

Cursed JavaScript hoisting!

This fixes test-partial-keyframes.html.
Remove superfluous TODO
Remove AnimationEffect.composite

The composite attribute is present on both KeyframeAnimationEffect and
PathAnimationEffect, but not the base class.
Merge pull request #298 from steveblock/partialKeyframes

Fix a bad rebase in normalizeKeyframeDictionary()
Merge pull request #297 from mithro/master

Fixing update-testcases and adding the thus missing test.
Merge pull request #299 from rjwright/nullTargetAnimations

Null target animations
Merge pull request #295 from steveblock/keyframeAnimationEffect

Follow-up fixes to updated KeyframeAnimationEffect
Fix script references in test-null-target
Add getters/setters for composite/accumulate and trigger re-ticks
Remove debugging and add nochecks to testcases
Merge pull request #300 from dstockwell/retick-composite-accumulate

Add getters/setters for composite/accumulate and trigger re-ticks
Merge pull request #301 from dstockwell/clean-up-tests

Remove debugging and add nochecks to testcases
Implement TimedItemList
Add '.pathSegList' to the example PathAnimationEffect call
Remove indexed getters/setters and length from TimingGroup