Adapt to support PDF.js v1.0.907

... as per #86.

Tested with:
 * Iceweasel 31.2.0 (Shipped with Debian, built on top of Firefox ESR) - ships with PDF.js v1.0.68
 * Firefox 31.3.0 (current ESR a.k.a. Extended Support Release) - ships with PDF.js v1.0.68
 * Firefox 34.0.5 (current stable) - ships with PDF.js v1.0.712
 * Firefox 34.0.5 (current beta - yes, it's the same as stable, just released) - ships with PDF.js v1.0.712
 * Firefox 35.0a2 (developer edition a.k.a. aurora a.k.a. alpha) - ships with PDF.js v1.0.907

According to tests, all involved PDF.js versions are now fully supported.

Okay sorry, my intention wasn't to have two methods here one aliased to the other. I had misunderstood that `applicable` was used in multiple places and under different contexts. What I wanted to fix was the method name `applicable` which I don't think is a very good method name, it is very unclear what is applicable to what when you see it in use.

This is clearly out of scope of this fix so if you want to merge the two back into one that's fine with me.