git-remote-mediawiki: better error message when HTTP(S) access fails

My use-case is an invalid SSL certificate. Pulling from the wiki with a
recent version of libwww-perl fails, and git-remote-mediawiki gave no
clue about the reason. Give the mediawiki API detailed error message, and
since it is not so informative, hint the user about an invalid SSL
certificate on https:// urls.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/mw-to-git/git-remote-mediawiki.perl

@@ -238,6 +238,22 @@ sub mw_connect_maybe {
 	}
 }
 
+sub fatal_mw_error {
+	my $action = shift;
+	print STDERR "fatal: could not $action.\n";
+	print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
+	if ($url =~ /^https/) {
+		print STDERR "fatal: make sure '$url/api.php' is a valid page\n";
+		print STDERR "fatal: and the SSL certificate is correct.\n";
+	} else {
+		print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
+	}
+	print STDERR "fatal: (error " .
+	    $mediawiki->{error}->{code} . ': ' .
+	    $mediawiki->{error}->{details} . ")\n";
+	exit 1;
+}
+
 ## Functions for listing pages on the remote wiki
 sub get_mw_tracked_pages {
 	my $pages = shift;
@@ -290,10 +306,7 @@ sub get_mw_all_pages {
 		aplimit => 'max'
 	});
 	if (!defined($mw_pages)) {
-		print STDERR "fatal: could not get the list of wiki pages.\n";
-		print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
-		print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
-		exit 1;
+		fatal_mw_error("get the list of wiki pages");
 	}
 	foreach my $page (@{$mw_pages}) {
 		$pages->{$page->{title}} = $page;
@@ -316,10 +329,7 @@ sub get_mw_first_pages {
 		titles => $titles,
 	});
 	if (!defined($mw_pages)) {
-		print STDERR "fatal: could not query the list of wiki pages.\n";
-		print STDERR "fatal: '$url' does not appear to be a mediawiki\n";
-		print STDERR "fatal: make sure '$url/api.php' is a valid page.\n";
-		exit 1;
+		fatal_mw_error("query the list of wiki pages");
 	}
 	while (my ($id, $page) = each(%{$mw_pages->{query}->{pages}})) {
 		if ($id < 0) {