Make IO#set_encoding with binary external encoding use nil internal encoding

This was already the behavior when a single `'external:internal'`
encoding specifier string was passed.  This makes the behavior
consistent for the case where separate external and internal
encoding specifiers are provided.

While here, fix the IO#set_encoding method documentation to
state that either the first or second argument can be a string
with an encoding name, and describe the behavior when the
external encoding is binary.

Fixes [Bug #18899]

0 files changed, 0 insertions, 0 deletions