Fixes to input validation and output escaping for user preferences.

Fixes to input validation and output escaping for user preferences.
Inserting a newline into some improperly filtered option strings could be used to overwrite other pref values, bypassing their input validation. Any newlines now get filtered out at User::setOption as a final line of defence.
There were a few HTML injection bugs, but none appear to be exploitable, as prefs can only be set if you already control the account.
Bug found by gmaxwell.