Fix for meta refresh tags

Meta refresh tags with an interval (regardless of how great) were still
being redirected automatically.  Also, a meta refresh with the URL
specified as the same (current) URL would result in an endless refresh -
some checks added.

Created an additional PhpBrowser config var 'refresh_max_interval' to
control the largest interval allowed for an auto redirect.

Created a new test case, and added to a couple existing test cases.
Merge pull request #1515 from zbateson/meta-refresh-tag-timeout-length

Fix for meta refresh tags