Get rid of leaflet.ie.css

[mourner]

As old IE versions get used less and less with time, and it's also time to drop at least IE6 support already, we can simplify some of the fallback rules in the current IE-only CSS (leaflet.ie.css), and move them to the main leaflet.css file (perhaps with the help of some hacks).

Once the IE-only CSS is small enough, there's not much point in keeping it in a separate file, and it also makes the Leaflet include code snipped much simpler by ditching the conditional comment.

I know IE targeting CSS hacks are considered a bad practice, but in this case, I think it's justified.

cc @tmcw @danzel

[tmcw]

+1, will /cc in css master @tristen

[danzel]

Very happy to drop IE6 support (I never test on it myself etc etc).
Definitely need to keep 7+ for the time being.

I'm not a huge fan of the _*\9 css hacks, they are just really ugly and hacky!

We could go for something like this:
http://www.paulirish.com/2008/conditional-stylesheets-vs-css-hacks-answer-neither/
and setting the class on the map element via js rather than via conditional comments (we already version detect oldie)
Which allows us to keep the css for old IE slightly separate, would take a bit more code though.

But really the _*\9 css hacks are probably ok.

[mourner]

The only reason that has kept me from dropping IE6 is that minimally supporting it doesn't require any effort atm, and there's not much legacy code to remove (a couple lines of CSS, png fix for marker icons and that's it probably).

[mourner]

I like the idea of putting the hacks under a .leaflet-oldie namespace. Much cleaner than the symbol hacks and I don't see any reasons not to do it.

[mourner]

Cleaned up and improved old IE stylesheets and moved them into the main CSS file (namespaced with .leaflet-oldie). Looks good?

[mourner]

Also dropped IE6-specific hacks. Leaflet isn't super-great on IE6 already so a couple less hacks won't make it much worse. And nobody cares.