The old solution made clicking on tabs (and other wide characters) always
put the cursor *before* them, even when clicking near their right.

Closes #703

Hide it by overlaying it with our fake scrollbar. Remove explicit wheel handling
for reasons of being extremely hard to get right.

Issue #694

Issue #698

Issue #698

And move browser detection up in the codemirror.js file, to prevent
further instances of 'use sniffing before actually doing it' bugs.

Closes #692

That'll make getElementById fail to return our measure element,
which shouldn't break the whole editor anymore now.

To prevent problems with script concatenation.

Closes #684

This fixes an error in the case that extra properties have been added to
the array prototype.

Closes #679

Issue #676

Issue #674

Issue #650