gitweb: Do not use bareword filehandles

gitweb: Do not use bareword filehandles

gitweb: Do not use bareword filehandles

The script was using bareword filehandles.  This is considered a bad
practice so they have been changed to indirect filehandles.

Changes touch git_get_project_ctags and mimetype_guess_file;
while at it rename local variable from $mime to $mimetype (in
mimetype_guess_file) to better reflect its value (its contents).

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>