Plugin functionality for User Registration validation schemes

[BrianKoontz]

Lightweight set of classes that permit run-time implementation of one or more registration validation schemes. Provides a set of minimal "hooks" (currently, URAuthDisplay() and URAuthVerify()) for usersettings.php. All underlying logic is contained in subclasses of URAuthTmpl (each validation scheme corresponds to a subclass of URAuthTmpl). Implementation of validation modules is entirely self-contained and requires nothing more than copying the desired UR module into libs/UR and enabling the necessary params in wikka.config.php. Multiple modules are "anded" together (i.e., all modules must validate as true for registration to be successful).

Related tickets: #496, #236, #606

[BrianKoontz]

(In [847]) Initial implementation, along with two verification modules (see comments in each module for instructions on how to deploy). Refs #609.

[BrianKoontz]

(In [848]) Fixed quoting problem in eval statement. Refs #609.

[BrianKoontz]

Tests successful for revision 863.

[BrianKoontz]

(In [1085]) Port of UR validation framework to trunk. Refs #496, #609