Add more errors to `checkExtractOptions`

[letFunny]

In this tests the error message should be more descriptive:

	summary: "Globbing must also have a single target",
	pkgdata: testutil.PackageData["test-package"],
	options: deb.ExtractOptions{
		Extract: map[string][]deb.ExtractInfo{
			"/etc/d**": []deb.ExtractInfo{{
				Path: "/etc/d**",
			}, {
				Path: "/etc/d**",
			}},
		},
	},
	error: `cannot extract .*: when using wildcards source and target paths must match: /etc/d\*\*`,
}, {
	summary: "Globbing cannot change modes",
	pkgdata: testutil.PackageData["test-package"],
	options: deb.ExtractOptions{
		Extract: map[string][]deb.ExtractInfo{
			"/d1/d**": []deb.ExtractInfo{{
				Path: "/d1/d**",
				Mode: 0777,
			}},
		},
	},
	error: `cannot extract .*: when using wildcards source and target paths must match: /d1/d\*\*`,