mac/make-package: behavior change

[Steven Tamm]

I just changed the behavior of make-package to by default perform the 
build in a temporary directory instead of in the source.  For the old 
behavior, add the option "--build-in-place".    A couple people had 
asked for it and since I regularly build both the X and the Carbon 
versions, I didn't want the source tree to be littered with .o files.  
I also made changes to src/Makefile to correctly create the Emacs.app 
if the build is done in a separate directory.

Here are the new options:

      --build-in-place    Build the application in the source directory
                          instead of a temporary directory.
      --build-dir=DIR     Build the application in the specified 
directory
                          instead of a temporary directory.  Mutually 
exclusive
                          with --build-in-place.

-Steven