updated release_notes.stex to describe the recent fixes for bugs that dated back to Version 8.4 or before and to combine the three performance subsections directly related to the new compiler back-end, since the changes all occurred between publicly available releases.
updated release_notes.stex to describe the recent fixes for bugs that
dated back to Version 8.4 or before and to combine the three performance
subsections directly related to the new compiler back-end, since the
changes all occurred between publicly available releases.

mflatt/ChezScheme,mflatt/ChezScheme,mflatt/ChezScheme