{% definevar %} can now store a value as a boolean or integer through

the as_type= argument. By default, this stored as a string

(equivalent to str).
When passing as_type=bool, a true (lowercased) or 1 will

result in a stored True. Anything else will be False.
When passing as_type=int, the value will be converted to an integer.

If the value can't be parsed as an integer, a TemplateSyntaxError will

be raised.
There's also an optimization around the options. We now convert to a

set so we don't repeatedly iterate through the list for each option.

Unit tests pass.
Made use of this in some in-progress code in Review Board for setting

options.