ifchanged doesn't properly reset itself if not evaluated each time through the loop

[Ned Batchelder]

When using ifchanged in a doubly-nested loop, the value is only reset to None on the inner loop's first iteration. But if the ifchanged tag is inside another conditional, it may not be evaluated on the first iteration. This can mean the value isn't properly reset:

{% for data in datalist %}

{% for c,d in data %}

{% if c %}

{% ifchanged %}{{ d }}{% endifchanged %}

{% endif %}

{% endfor %}

{% endfor %}

The fix is to not examine forloop.first explicitly, but to annotate the forloop context.

[Ned Batchelder]

the patch!