Error messages are not always cleared, resulting in duplicated messages.

[TheWitness]

Describe the bug

If you are on a page, and encounter an error on the form, and then go off and try and render another form, the error message persists and sometimes indefinitely or until the session is cleared.

To Reproduce

Steps to reproduce the behavior:

1. Goto a page that has form validation

2. Edit the form and create an error

3. Do on correct the error, but goto another page where a form is being rendered like CDEF Edit for example.

4. See error

Expected behavior

Cacti should not persist this session variable for longer than it has to. It should present the right error messages for each page you are visiting.