Implement esnprintf() and make formatted calls more efficient

Within the components, snprintf() was unchecked and had inefficient
calls in some places.
We implement esnprintf() that does all the dirty laundry for us
and use it exclusively now.

util.h

@@ -8,6 +8,7 @@ extern char *argv0;
 void warn(const char *, ...);
 void die(const char *, ...);
 
+int esnprintf(char *str, size_t size, const char *fmt, ...);
 const char *bprintf(const char *fmt, ...);
 const char *fmt_scaled(size_t);
 int pscanf(const char *path, const char *fmt, ...);