When "-XclassesAsDecls" is used and I try to load a class that refers to non-existent annotation,
the class fails to load. The following part of APT (in JavaCompiler.java) fails by throwing
Symbol.CompletionFailure.

if (! l.head.endsWith(".java") ) { // process as class file
ClassSymbol cs = reader.enterClass(names.fromString(l.head));
try {
cs.complete();
} catch(Symbol.CompletionFailure cf) {
bark.error(Position.NOPOS, "CantFindClass", l);
continue;
}

At the point of this failure cf.toString() says "com.sun.tools.javac.code.Symbol$CompletionFailure: file javax\xml\bind\annotation\XmlElement.class not found" (this is the name of the annotation that I didn't include
in my classpath), so CompletionFailure exception does have the correct information as to what went wrong.

However, the next line doesn't use this detailed information for error report. It will just say:

    error: Could not find class file for abc.Test

even though this class was indeed found --- it's the javax.xml.bind.annotation.XmlElement that wasn't found.

This causes the user to waste time on checking and double-checking that abc/Test.class does exist, without making
them realized that what they are missing is an entirely different class.

I hope cf.getMessage() will be used as a part of the error message.