int64_t in stringutils

[Philippe Torrelli]

Hello,

Trying to compile recent version of minisip, 
libmcrypto/Init.cxx can't be built anymore because  int64_t is 
not defined .
In visual studio, int64_t needs to be defined explicitely. 

I had no problem on linux because after include <string> , the 
 type int64_t is typedef'ed.

Many files include stringutils.h after having included 
something that includes mtypes.h,  but MemOject.h does not.

As the type is directy used the header, it wouldn't hurt to 
include mtypes.h in stringutils.h 
( it was the case when atoi was in a separate header ).

Suggestion:
#include<libmutil/mtypes.h>
in 
#include<libmutil/stringutils.h>