#2 check for binary content fails

[Gregor Goldbach]

The check for binary data (function
inbuf_contains_binary() in file parse_tools.c) in the
first chunk of data read from the server fails if the
page uses a non-English encoding.

The check is done with simple calls to isprint() and
isspace(). If the content is e.g. German this fails
although the encoding of the page is set correctly.
This is because the current locale is not changed.

Bugfix: extract the encoding from the HTTP header of
the document and set the locale.