get name of a member of a structure
id - structure type ID
member_offset - member offset. The offset can be
any offset in the member. For example,
is a member is 4 bytes long and starts
at offset 2, then 2, 3, 4, 5 denote
the same structure member.
returns: 0 if bad structure type ID is passed
or no such member in the structure
otherwise returns name of the specified member.
string get_member_name(long id, long member_offset);