gitweb: Allow UTF-8 encoded CGI query parameters and path_info

gitweb: Allow UTF-8 encoded CGI query parameters and path_info

Gitweb forgot to turn query parameters into UTF-8. This results in a bug
that one cannot search for a string with characters outside US-ASCII.  For
example searching for "Michał Kiedrowicz" (containing letter 'ł' - LATIN
SMALL LETTER L WITH STROKE, with Unicode codepoint U+0142, represented
with 0xc5 0x82 bytes in UTF-8 and percent-encoded as %C5%82) result in the
following incorrect data in search field

	MichaÅ\202 Kiedrowicz

This is caused by CGI by default treating '0xc5 0x82' bytes as two
characters in Perl legacy encoding latin-1 (iso-8859-1), because 's'
query parameter is not processed explicitly as UTF-8 encoded string.

The solution used here follows "Using Unicode in a Perl CGI script"
article on http://www.lemoda.net/cgi/perl-unicode/index.html:

	use CGI;
	use Encode 'decode_utf8;
	my $value = params('input');
	$value = decode_utf8($value);

Decoding UTF-8 is done when filling %input_params hash and $path_info
variable; the former requires to move from explicit $cgi->param(<label>)
to $input_params{<name>} in a few places, which is a good idea anyway.

Also add -override=>1 parameter to $cgi->textfield() invocation in search
form.  Otherwise CGI would use values from query string if it is present,
filling value from $cgi->param... without decode_utf8().  As we are using
value of appropriate parameter anyway, -override=>1 doesn't change the
situation but makes gitweb fill search field correctly.

We could simply use the '-utf8' pragma (via "use CGI '-utf8';") to solve
this, but according to CGI.pm documentation, it may cause problems with
POST requests containing binary files, and it requires CGI 3.31 (I think),
released with perl v5.8.9.

Reported-by: Michał Kiedrowicz <redacted>
Signed-off-by: Jakub Narębski <redacted>
Tested-by: Michał Kiedrowicz <redacted>
Signed-off-by: Junio C Hamano <redacted>