"Specified by:" and "Overrides:" should exist & point to ext. referenced classes

[This bug is re-written from bug 4854934]

It appears that when method A.m overrides method in external referenced class B,
the "Overrides:" section is not generated (but should be). That is, if B is not
passed in on the command line, javadoc does not create the "Overrides:" section
for method m. If B is passed in, then it does create the "Overrides:" section.

Example: Given this source file with method read() that overrides
"public int read()" in FilterReader:

---------------- XReader.java ---------------------
public class XReader extends java.io.FilterReader {
  /**
   * This is a doc comment
   */
   public int read() {
      return 'W';
   }
}
---------------------------------------------------

Generate the HTML documentation using Javadoc 1.4.2-beta:

javadoc -d html XReader.java

The generated HTML documentation for XReader.read()
is missing any "Overrides:" labels. It actually looks
like this:

-----------------------------
read

public int read()

   This is a doc comment
------------------------------

It should instead look like this, with override labels:

-----------------------------
read

public int read()

   This is a doc comment

Overrides:
   read in class FilterReader
   ~~~~ ~~~~~~~~~~~~
------------------------------

Adding the -link or -linkoffline option makes no difference --
the labels and links still do not appear when trying this:

javadoc -d html -linkoffline "http://java.sun.com/j2se/1.4/docs/api" . XReader.java

In this case, "read" should be a link to java/io/FilterReader.html#read()
and "FilterReader" should be a link to java/io/FilterReader.html,
identical to this J2SE class that extends FilterReader:

http://java.sun.com/j2se/1.4.1/docs/api/java/io/PushbackReader.html#read()

The presence of these labels and links should be independent
of inheriting doc comments.

FWIW, I tested for the presenece of "Specified by:" when implementing
an external referenced class (to see if it's a problem), and it works
just fine, producing "Specified by:" labels and links. Here's that source
file:

----------------- XComparable.java -----------------------
public class XComparable implements java.lang.Comparable {
   public int compareTo(Object o) {
      return 'W';
   }
}
--------------------------------------------------------