(name_gather, addname): Use offsetof when computing sizes for

(name_gather, addname): Use offsetof when computing sizes for
struct hack; this avoids wasted space in some cases.
(name_gather): Use strcpy, not memcpy.
for consistency with other code that does similar things.
(read_name_from_file, name_next, name_gather, add_hierarchy_to_namelist):
Avoid quadratic behavior when reallocating buffers.
Check for buffer size overflow.
(addname): Avoid unnecessary clearing of memory.