library/io.m:
As above.
library/io.error_util.m:
Delete the equivalent operation is_success/1 from here and
just use system_error_is_success/1 instead.
NEWS.md:
Announce the new predicate.
This reduces the size of io.m a bit. The other reason for moving the
code is to allow modules that occur in a dependency cycle with io.m
to read results from io.error_util.trans_opt, whereas they may have
been prevented from reading io.trans_opt.
library/io.m:
library/io.error_util.m:
Move is_error, throw_on_error and other similar predicates to a
new undocumented submodule of io.m.
Also move the support functions/predicates used by those predicates.
Make io.make_io_error_from_system_error and
io.make_io_error_from_windows_error call the implementations in
io.error_util.m.
library/MODULES_UNDOC:
library/library.m:
List the new submodule as undocumented.
library/benchmarking.m:
library/bitmap.m:
library/dir.m:
library/io.call_system.m:
library/io.file.m:
Import the new submodule.
