Suppress warnings for patterns.

This seems to be triggered when the attribute is not set or some
corner case when the value passed is undef (this latter couldn't be
reproduced).
Use Test::Warnings instead of local $SIG{__WARN__}
Merge pull request #60 from melmothx/topic/fix-undef-warnings-in-patterns

Suppress warnings for patterns.
Fix POD example on accepting empty dates in the date filter.
Fix next and count calls in Template::Pager class.
Fix name of pager module in Template::Flute::Pager's POD.
Fix pager check in _paging method.
Add test for simple append with joiner.