Fix for #4707/#7101

[csnover]

Original commit for #4707 was incomplete and would only not clobber existing filters if one of those existing filters happened to be the opacity filter. New bug #7101 was raised about this. This patch ensures existing filters are not clobbered even if opacity filter does not exist.

Because my previous ajax pull request didn’t get committed upstream, this pull request is a bit fucked and includes 4 of my commits… sorry about that. I will try to learn for the future how to use this thing properly so it only pulls one commit instead of a range. :|

[jeresig]

Landed! In the future you should make a separate branch for each bug fix that you make - this will avoid problems like this (and make it easier for me to land the change).

[tpreusse]

I just notices you used
style.filter +' '+ opacity
this might have some disadvantages over using
filter +' '+ opacity
and could lead to different behaviour depending on whether a alpha filter has been applied before or not since for the true case
filter.replace(ralpha, opacity)
local filter variable is used and not style.filter

Thomas

[csnover]

filter is defined as style.filter || "" so there should be no behavioural difference unless style.filter is somehow null or undefined. It may be a better idea from a code size standpoint to use filter instead, though.

[tpreusse]

You'r right I was looking at 1.4.2 where it was defined as
var filter = style.filter || jQuery.curCSS( elem, "filter" ) || "";