[rfa] make clean should remove observe.h and observer.inc

[Tom Tromey]

Michael> 2011-02-23  Michael Snyder  <msnyder@vmware.com>
Michael> 	* Makefile.in (clean): Make clean should remove generated files
Michael> 	observer.h and observer.inc.

I think this is ok.

There is a sort of GNU rule governing "clean" behavior.  I'm not sure
whether this is documented in the GNU standards but it is longstanding
practice, existing before and then codified in Automake:

* 'mostlyclean' is a "useful" subset of 'clean'
* If 'make' built it, 'clean' removes it
* If 'configure' built it, 'distclean' removes it
* If the developer built it, but it is a generated file not needed for
  "configure; make", then `maintainer-clean' removes it.

I looked a little more and I found this in the Automake manual's "Clean"
node.

Tom