Slightly improve previous commit that silenced a Clang Scan warning.

The strdup() call does not take advantage of the known length of the
source string. Replace by malloc() and memcpy() utilizimng the pre-
calculated string length.

Submitted by:	cperciva
Reported by:	rgrimes
MFC after:	2 weeks

lib/libfigpar/string_m.c

@@ -119,9 +119,10 @@ replaceall(char *source, const char *find, const char *replace)
 
 	/* If replace is longer than find, we'll need to create a temp copy */
 	if (rlen > flen) {
-		temp = strdup(source);
+		temp = malloc(slen + 1);
 		if (temp == NULL) /* could not allocate memory */
 			return (-1);
+		memcpy(temp, source, slen + 1);
 	} else
 		temp = source;