MINOR: tools: add very basic support for composite pointers

MINOR: tools: add very basic support for composite pointers

Very often we want to associate one or two flags to a pointer, to
put a type on it or whatever. This patch provides this in standard.h
in the form of a few inline functions which combine a void * pointer
with an int and return an unsigned long called a composite address.
The functions allow to individuall set, retrieve both the pointer and
the flags. This is very similar to what is used in ebtree in fact.