should use click event instead of mousedown

[btmorex]

Piwik click tracking should use the click event instead of the mousedown event because:

1.) mousedown is not the same as a click and it should be tracking clicks.

2.) The current way of doing things prevents the right-click menu from appearing until the tracking code has run, which can take a long time for downloads or external links.

[vipsoft]

Yes, this is inconsistent from the GA, MS, and Y! tracking code.

While this is already moot in the new piwik.js under development -- the delay is deferred to the unload -- I will change this to be consistent with other trackers.

[vipsoft]

(In [1151]) fixes #355 - OO version of piwik.js which no longer modifies DOM; remove misc/testJavascripTracker (interactive tests); add tests/javascript (QUnit unit tests); fixes #661 - use click event instead of mousedown; fixes #549 - define your own download/outlink tracking classes; fixes #82 - add hook interface for module