include strings.h where appriopriate...

instead or additionally to string.h, in preparation for functions move.
* moves str[n]casecmp() functions and others to strings.h.
* strings.h doesn't include string.h anymore.
* this solves #10949

src/bin/open.cpp

@@ -19,7 +19,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <strings.h>
 
 #include <Entry.h>
 #include <List.h>