rewrite some assertions for better readability

Some assertions are written as "if (x) assert(0)" to avoid having
the text of a long argument compiled in the binary. Rewrite them
to use a new BRIEF_ASSERT macro to make the condition easier to read in
its non-negated form and make it easier to turn it back to the full-text
assert if needed.

util.h

@@ -272,4 +272,12 @@ extern int UTI_SplitString(char *string, char **words, int max_saved_words);
 
 #define SQUARE(x) ((x) * (x))
 
+/* Macro to make an assertion with the text of a long argument replaced
+   with "0" to avoid bloating the compiled binary */
+#ifdef NDEBUG
+#define BRIEF_ASSERT(a)
+#else
+#define BRIEF_ASSERT(a) if (!(a)) assert(0)
+#endif
+
 #endif /* GOT_UTIL_H */