Fixed a resizing bug on IE.

On IE resize events can be sent very early, with the result that the
window is not correctly resized. It may end up with a non-zero scrolling
offset, which throws off subsequent computations.
Styling fix for IE.
Use browsers.txt to obtain the list of browsers.
Made after_scenario a bit more robust.
Prevent deletion of secondary targets.
Fixed a validator bug.

A piece of code was erroneously using `classList`, which does not exist
for XML nodes in IE.
Removed an old pointless bit of code.
Note a future change.
Version bump.
Merge branch 'release/0.20.2'
Merge tag 'v0.20.2' into develop

0.20.2