allow THAllocator to have a NULL realloc
allow THAllocator to have a NULL realloc

Moodstocks/torch7,Moodstocks/torch7,adamlerer/torch7,adamlerer/torch7,colesbury/torch7,szagoruyko/torch7,diz-vara/torch7,colesbury/torch7,diz-vara/torch7,szagoruyko/torch7