support for dynamic variables in the report_view page

[andrei2102@…]

After the discussion on this trac-dev thread I made a patch that displays a list of filters for every variable in a query.

The problem this patch resolves is encountered when a sql report has a variable defined and no values is passed in the URL. The patch allows the user to enter values for this variables.

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Patch against 0.11-stable adding editable fields for report arguments

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The patch above is a rework of the first patch attached (which was already very good):

• The layout of the argument fieldset was adapted to be as close to the custom query as possible.
• A warning lists missing arguments (if any).
• The folding JavaScript is not called if there are no arguments.

Fields are considered missing if they don't appear in the request at all. Empty arguments are considered present.

Comments?

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Patch applied in [7555], with a few fixes to report test cases, and an additional test case for missing arguments.