If someone on whatever reasons uses --default-character-set=cp850,
this will avoid incorrect display, and inserting incorrect data.

Adjusting console codepage sometimes also needs to happen with
--default-charset=auto, on older Windows. This is because autodetection
is not always exact. For example, console codepage on US editions of
Windows is 437. Client autodetects it as cp850, a rather loose
approximation, given 46 code point differences. We change the console
codepage to cp850, so that there is no discrepancy.

That fix is currently Windows-only, and serves people who used combination
of chcp to achieve WYSIWYG effect (although, this would mostly likely used
with utf8 in the past)

Now, --default-character-set would be a replacement for that.

Fix fs_character_set() detection of current codepage.