test/feh.t: Give a proper error if PACKAGE / VERSION are undefined

my ($feh_name, $feh_version) = @ENV{'PACKAGE', 'VERSION'};

my $err_no_env = <<'EOF';

Unable to determine feh PACKAGE or VERSION.

This is most likely because you ran 'prove test' or 'perl test/feh.t'.

Sinc this test uses make variables and is therefore designed to be run from

the Makefile only, use 'make test' instead.

If you absolutely need to run it the other way, use

    PACKAGE=feh VERSION=1.5 ${your_command}

(with the appropiate values, of course).

EOF

if (length($feh_name) == 0 or length($feh_version) == 0) {

	die($err_no_env);

}

my $re_warning =

	qr{${feh_name} WARNING: test/fail\.... \- No Imlib2 loader for that file format\n};

my $re_loadable = qr{test/ok\....};