Make sure strcasecmp() is declared.

On recent glibc versions strings.h is not included by default, so the compiler
will issue a warning for implicit declaration of strcasecmp().
patch by Diego 'Flameeyes' Pettenò, flameeyes gmail com

Originally committed as revision 15531 to svn://svn.ffmpeg.org/ffmpeg/trunk

vhook/imlib2.c

@@ -53,6 +53,7 @@
 #include <fcntl.h>
 #include <stdarg.h>
 #include <string.h>
+#include <strings.h>
 #include <unistd.h>
 #undef time
 #include <sys/time.h>