Update memory tracking/debugging reference

docs/INTERNALS

@@ -437,12 +437,23 @@ Memory Debugging
  after a complete session,
 
  memanalyze.pl is the perl script present only present in CVS (not part of the
- release archives) that analyzes a log file generated by the memdebug
+ release archives) that analyzes a log file generated by the memory tracking
  system. It detects if resources are allocated but never freed and other kinds
  of errors related to resource management.
 
- Use -DMALLOCDEBUG when compiling to enable memory debugging, this is also
- switched on by running configure with --enable-debug.
+ Internally, definition of preprocessor symbol DEBUGBUILD restricts code which
+ is only compiled for debug enabled builds. And symbol CURLDEBUG is used to
+ differentiate code which is _only_ used for memory tracking/debugging.
+
+ Use -DCURLDEBUG when compiling to enable memory debugging, this is also
+ switched on by running configure with --enable-curldebug. Use -DDEBUGBUILD
+ when compiling to enable a debug build or run configure with --enable-debug.
+
+ curl --version will list 'Debug' feature for debug enabled builds, and
+ will list 'TrackMemory' feature for curl debug memory tracking capable
+ builds. These features are independent and can be controlled when running
+ the configure script. When --enable-debug is given both features will be
+ enabled, unless some restriction prevents memory tracking from being used.
 
 Test Suite
 ==========

lib/config.dos

@@ -101,7 +101,8 @@
 
 #define BSD
 
-/* #define MALLOCDEBUG */
+/* CURLDEBUG definition enables memory tracking */
+/* #define CURLDEBUG */
 
 /* USE_ZLIB on cmd-line */
 #ifdef USE_ZLIB