patterndb: Allow a wider range of characters in a class value

Allow a wider range of characters in a class value. To the already
existing list, the following were added (both pdb3 and pdb4): "%",
":", "@", "+", "!", "^", "/" and "\". This should hopefully cover most
- if not all - the usual suspects.

Requested-by: Evan Rempel <erempel@uvic.ca>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>