* linux-low.c (linux_read_memory): Change return type to
int. Check for and return error from ptrace().
* target.c (read_inferior_memory): Change return type to int. Pass
back return status from the_target->read_memory().
* target.h (struct target_ops): Adapt *read_memory() prototype.
Update comment.
(read_inferior_memory): Adapt prototype.
* server.c (main): Return an error packet if
read_inferior_memory() returns an error.