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.
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
First attempt at a "real time" mode.

 (Previously called "manual" mode.)