Implement DeclareError|DeclareWarning statements

[lisachenko]

An aspect may specify that a particular join point should never be reached.

/**
 * @DeclareError(Pointcut)
 */
protected static $errorMessage = 'This is an error message';

/**
 * @DeclareWarning(Pointcut)
 */
protected static $warningMessage = 'This is a warning message';

If the compiler determines that a join point in Pointcut could possibly be reached, then it will signal either an error or warning, as declared, using the string for its message.

The general form of the statement is this: "Declare it to be a runtime warning/error, if any join point matching the following pointcut expression occurs, and this is the warning message I'd like you to use."