gitweb: die when a configuration file cannot be read

gitweb: die when a configuration file cannot be read

Fix a possibility of a permission to access error go unnoticed.

Perl uses two different variables to manage errors from a "do
$filename" construct. One is $@, which is set in this case when do
is unable to compile the file. The other is $!, which is set in case
do cannot read the file.  The current code only checks "$@", which
means a configuration file passed to GitWeb that is not readable by
the server process does not cause it to "die".

Make sure we also check and act on "$!" to fix this.

Signed-off-by: Marcelo Roberto Jimenez <marcelo.jimenez@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>