#include <IO.h> int write_rname( GapIO *io, int rnum, char *name);
This writes a new reading name name for reading number rnum.
This updates both the disk and memory copies of the reading structure and the
reading name cache, using the gel_write and io_wname functions.
If reading rnum does not exist, it is created first using the
io_init_reading function.
It returns 0 for success and -1 for failure.