ALPHANUMERICP
=============

Syntax: (alphanumericp <character>)

This function checks, whether the argument is an
alphanumeric character. It returns T, when the test 
was successful, otherwise NIL.

uppercase-character:                   A...Z
lowercase-character:                   a...z
digit-character:                       0...9
alphanumeric-character:                A...Z, a...z
                                       and 0...9

example:       >(alphanumericp #\!)
               NIL