Tweak Flymake commands flymake-goto-[next/prev]-error

Tweak Flymake commands flymake-goto-[next/prev]-error

Add filters, useful for backends like the upcoming
flymake-elisp-checkdoc backend, for example, which litters everything
with low-priority notes.

Also re-implement wraparound for flymake-goto-next-error. Manual
mentions this, so it's probably a good idea to keep it.  Added a new
customization variable flymake-wrap-around to control it.

* lisp/progmodes/flymake.el (flymake-goto-prev-error)
(flymake-goto-next-error): Accept FILTER argument.
(flymake-wrap-around): New variable.
(flymake-goto-next-error): Wrap around according to flymake-wrap-around.

* test/lisp/progmodes/flymake-tests.el
(different-diagnostic-types, dummy-backends): Pass FILTER to
flymake-goto-prev-error.
(different-diagnostic-types)
(dummy-backends): Use flymake-wrap-around.