misleading install instruction in emacs/mac/INSTALL

[Gilbert Harman]

On a new intel iMac running Mac OS system 10.4.8, from the files in the new
pretest tarball:

In seeming accordance with the instructions in emacs/mac/INSTALL,
I ran:

./configure --with-x --enable-carbon-app
make
sudo make install

This produced a version that appears to run OK in the Mac window system but
/usr/local/bin/emacs did not run in X windows.  Apparently it is necessary
to do two installations, one using

./configure --enable-carbon-app

the other using

./configure --with-X --without-carbon-app

  Gil