Add PRIVPOL warning

This is an initial commit - this feature is in testing and is not ready
for deployment.

Warns users adding IP-address-like-text to a comment to adhere to the
Wikimedia Foudnation's Privacy Policy and policy on retention of personally
identifying information.
Fix syntax error
I've forgotten how to PHP
Remove duplicated assignment
Fix some silly errors
Trying to fix broken form layout
ffs
Let's try a dirty hack....

Don't judge me.
General fixes
Show a proper error message, expand on warning.
Reword some of the warning, fix comment preservation
Also match against IPv6, add to comment-quick
Merge branch 'privpol-enforcement', fixes #165