bug#33053: scm_i_mirror_backslashes assumes ASCII-compatible locale encoding

[Mark H Weaver]

The 'scm_i_mirror_backslashes' in load.c operates on C strings in the
locale encoding, and assumes that the locale encoding is ASCII
compatible.  In the Shift_JIS encoding, used in the "JP_jp.sjis" locale,
backslash '\' is mapped to a multibyte character, and the Yen sign '¥'
is represented using code 0x5C, the same code as backslash '\' in ASCII.

As a result, users of the "JP_jp.sjis" locale will have Yen signs '¥' in
their file names converted into slashes by this function.

     Mark