Fix reference to debugging-related README file in README and Makefile.dj

* README: Change README.debugging to debugging.html.
* Makefile.dj (OTHER_FILES): Likewise.

Makefile.dj

@@ -66,7 +66,7 @@ OTHER_FILES= PCR-Makefile OS2_MAKEFILE NT_MAKEFILE BCC_MAKEFILE \
            doc/README.amiga doc/README.win32 doc/README.cords \
            doc/README.rs6000 README.QUICK TODO tools/callprocs.sh \
            pc_excludes barrett_diagram doc/README.OS2 doc/README.Mac \
-           extra/MacOS.c EMX_MAKEFILE doc/README.debugging \
+           extra/MacOS.c EMX_MAKEFILE doc/debugging.html \
            extra/Mac_files/datastart.c extra/Mac_files/dataend.c \
            extra/Mac_files/MacOS_config.h \
            tools/add_gc_prefix.c doc/README.solaris2 doc/README.sgi \

README

@@ -142,7 +142,7 @@ to be disregarded, greatly reducing the probability of accidental
 retention of large objects.  For most purposes it seems best to compile
 with ALL_INTERIOR_POINTERS and to use GC_malloc_ignore_off_page if
 you get collector warnings from allocations of very large objects.
-See README.debugging for details.
+See debugging.html for details.
 
   WARNING: pointers inside memory allocated by the standard "malloc" are not
 seen by the garbage collector.  Thus objects pointed to only from such a