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/ircaux.h

@@ -16,10 +16,6 @@
 #include "irc.h"
 #include "irc_std.h"
 #include <stdio.h>
-#ifdef WANT_TCL
-#undef USE_TCLALLOC
-#include <tcl.h>
-#endif
 
 typedef int comp_len_func (char *, char *, int);
 typedef int comp_func (char *, char *);