Minor fixes to enable compiling against TCL8.5

Define USE_NON_CONST so that the newer TCL headers define functions in the
same way as pre-8.4 TCL headers.  It will be a good idea to change to
USE_COMPAT_CONST instead at some point.

Also use ckfree() instead of free() to free an allocation returned by TCL.

include/tcl_bx.h

@@ -26,7 +26,7 @@ void tcl_load (char *, char *, char *, char *);
 
 #ifdef WANT_TCL
 
-
+#define USE_NON_CONST
 #include <tcl.h>
 extern Tcl_Interp *tcl_interp;
 void check_tcl_tand (char *, char *, char *);