incremental compilation of langtools does not work

[Jonathan Gibbons]

This one took a while to track down.

I've been using the new build to debug javac and javadoc.
The build is nothing out of the oridinary, and I was building
the "images" target.

I added some print statements to javac/javadoc classes, but
some were not being executed. Eventually, in desperation, I
did a "make clean images".   All my print statements now worked.

So, it seems to me that changes to my langtools source files
don't make it all the way through to tools.jar.  Classes that end up
in rt.jar do get updated correctly.

To reproduce, try adding/removing print statements like the following
to important javac/javadoc classes:
     static { System.err.println("<init> JavadocTool"); }

-- Jon