ifequal and ifnotequal failing with negative numbers

that should have been:

{% ifnotequal -1 -5 %}
hello
{% endifnotequal %}

prints nothing

This patch doesn't handle the case of {% ifequal foo -elephant %} sensibly. It will try to process "-elephant" as if it were a number. I realise that is an error in any case, but we shouldn't confuse things further.

Straightforward enough.

We run this piece of code a *lot* (for every argument in every template tag), so speed is important. I'm going to hold off committing whilst I do some timing tests on different approaches. No need to rewrite the patch in any way -- it's correct on a functional level. I just want to try out a few options whilst we're playing in this area.

The reg-exp seems to be fastest here. I tried a couple of ways of removing the double scan over the string in the case of numbers (we do a reg-exp pass and then a pass for '.'), but it added more code than speed-ups and wasn't worth it.

(In [4690]) Fixed #3670 -- Fixed template argument parsing so that it understands negative floats and integers as numeric types. Patch from SmileyChris?.