Use OpenSSL's md5-implementation instead of UDT's own.

Rejected by author because of concerns for Windows computers
and mobile devices.

--- src/common.cpp	2011-12-26 12:09:11.000000000 -0500
+++ src/common.cpp	2012-01-26 17:48:01.000000000 -0500
@@ -56,5 +56,5 @@
 
 #include <cmath>
-#include "md5.h"
+#include <openssl/md5.h>
 #include "common.h"
 
@@ -742,8 +742,4 @@
 void CMD5::compute(const char* input, unsigned char result[16])
 {
-   md5_state_t state;
-
-   md5_init(&state);
-   md5_append(&state, (const md5_byte_t *)input, strlen(input));
-   md5_finish(&state, result);
+   MD5((const unsigned char *)input, strlen(input), result);
 }