gitweb: Better support for non-CSS aware web browsers

gitweb: Better support for non-CSS aware web browsers

Add option to replace SPC (' ') with hard (non-breakable) space HTML
entity ' ' in esc_html subroutine.

Replace ' ' with ' ' for the code/diff display part in git_blob
and git_patchset_body; this is to be able to view code and diffs in
web browsers which doesn't understand "white-space: pre;" CSS
declaration.

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