[patch] Make ifchanged tag accept a parameter

[wolfram@…]

The patch allows to pass a parameter to ifchanged, which is then evaluated and checked if it has changed, instead of the tag’s content. If it has changed the content is being printed, as usual. I.e. you can do

{% ifchanged variable %}print if variable's value has changed{% ifchanged %}

To know more about the details, ​read here.

[Wolfram Kriesing]

A little more explaination may be. In my case I had nested for loops and wanted to check if the outer had changed and modify something inside the inner loop.
That was impossible using ifchanged without telling what to look for if it had changed, so I enhanced ifchanged's syntax.
I hope you find it useful too.
Having ifchanged accept a parameter would be phantastic. Like so:

{% for country in countries %}
    {% for city in country.cities %}
        <div class="city{% ifchanged country %}Alternate{% endifchanged %}">
            {{ city.name }}
        </div>
    {% endfor %}
{% endfor %}

The ifchanged tag should be able to check if a certain variable has changed if given, otherwise work as usual.

[wolfram.kriesing@…]

The following updated patch allows for multiple parameters, such as:

{% ifchanged date.hour,date.date %}

Examples, doc and tests included.

[Jacob]

(In [4050]) Fixed #2800: the ifchanged tag now can optionally take paramaters to be checked for changing (instead of always using the content). Thanks, Wolfram Kriesing.

[anonymous]

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