checks amount of data ready to be read
int SP_equal_group_ids( group_id g1, group_id g2);
allows an application to determine if two specific instantiations of
a group are identical. This is not just if the memberships are identical, but rather
whether the two group ids represent the exact same group membership view at the same
point in time in the history of the group.
returns true (i.e. not 0) if the two group ids passed to it are equal.
It returns false if they are not equal.
Returns true (not 0 ) if they are equal and false if they are different.