[PATCH] format support for cache manager actions

This adds support for multiple output formats in the manager actions.

As discussed earlier it makes use of the file extension concept.

For example: /action.html

Would pass "html" in the format parameter. If the action is able to
produce HTML output, it can test for this format type and do so. The
default format is "txt" for backward compatibility.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE9 or 3.1.14
   Beta testers wanted for 3.2.0.10