util.c: I've added a function called mem_dup(). Similar to strdup(),

util.c:  I've added a function called mem_dup().  Similar to strdup(),
         mem_dup() allocates the required memory before copying the
         source data.  It returns NULL if memory could not be allcoated,
         else a pointer to the newly allocated memory.
proto.h: Rebuilt to add the prototype for mem_dup().
(This used to be commit 7f7e265ab457d046441d502d4b8447bc2c966675)