Centralise TRUE and FALSE definitions into defs.h.

This removes a lot of pointless duplications of those constants.

Of course, _ideally_, I should upgrade to C99 bool throughout the code
base, replacing TRUE and FALSE with true and false and tagging
variables explicitly as bool when that's what they semantically are.
But that's a much bigger piece of work, and shouldn't block this
trivial cleanup!

misc.h

@@ -13,13 +13,6 @@
 #include <stdarg.h>		       /* for va_list */
 #include <time.h>                      /* for struct tm */
 
-#ifndef FALSE
-#define FALSE 0
-#endif
-#ifndef TRUE
-#define TRUE 1
-#endif
-
 unsigned long parse_blocksize(const char *bs);
 char ctrlparse(char *s, char **next);