gitweb: Fix displaying unchopped argument in chop_and_escape_str

Do not use esc_html to escape [title] _attribute_ of a HTML element,
and quote unprintable characters.  Replace unprintable characters by
'?' and use CGI method to generate HTML element and do the escaping.

This caused bug noticed by Martin Koegler,
  Message-ID: <redacted>
that for bad commit encoding in author name, the title attribute (here
to show full, not shortened name) had embedded HTML code in it, result
of quoting unprintable characters the gitweb/HTML way. This of course
broke the HTML, causing page being not displayed in XML validating web
browsers.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>