Fix the check_latex script.

The addition of the requirement of PG files for hardcopy (namely the
`pg.sty` file), means that the `check_latex` script needs to know where
the pg directory is.  So find that the same way the webwork2 app does.

This fixes issue openwebwork#2543.

bin/check_latex

@@ -27,9 +27,17 @@ use feature 'say';
 
 BEGIN {
 	use Mojo::File qw(curfile);
-	use Env qw(WEBWORK_ROOT);
+	use YAML::XS qw(LoadFile);
+	use Env qw(WEBWORK_ROOT PG_ROOT);
 
-	$WEBWORK_ROOT = curfile->dirname->dirname;
+	$WEBWORK_ROOT = curfile->dirname->dirname->to_string;
+
+	# Load the configuration file to obtain the PG root directory.
+	my $config_file = "$WEBWORK_ROOT/conf/webwork2.mojolicious.yml";
+	$config_file = "$WEBWORK_ROOT/conf/webwork2.mojolicious.dist.yml" unless -e $config_file;
+	my $config = LoadFile($config_file);
+
+	$PG_ROOT = $config->{pg_dir};
 }
 
 use File::Temp qw(tempdir);