Add check for incorrect use of 'access callback'

Several modules were incorrectly updated to the D6 menu API, resulting in security vulnerabilities (SA-2008-063). Coder should check for this apparently quite common mistake. Here's a rule based on the regex that pwolanin used to find the vulnerable modules (although there were a small number of false positives).

I'm not sure if this belongs in the 6x review or the security review; the attached patch puts it in 6x.