My recent change added some control over stripping to {% definevar %}

and made stripping mandatory for {% attr %}. This change builds upon

that by refining the behavior and adding more options.
{% attr %} now condenses the whitespace within the value by default

(turning sequences of spaces, tabs, and newlines into a single space).

All the new behavior can be turned off with the "nocondense" option.
It also now marks the value as unsafe, instead of making that the

caller's responsibility.
{% definevar %} now has a strip option for stripping

leading/trailing whitespace (replacing the new stripped), a

spaceless option for making the text spaceless (equivalent to wrapping

the value within as {% spaceless %}), and an unsafe option for

marking the value as unsafe.
Along with this (and to support these options), @blocktag now works with

template tags taking *args. When found, the check for the maximum number

of arguments will be turned off.

Unit tests passed.