Quilt can't locate Minecraft when the classpath is passed via a `Class-Path` manifest value

[sschr15]

When attempting to load Minecraft without a jar being explicitly passed or found in FS, Quilt looks to the classpath. It fails, however, if the classpath is a single jar containing a Class-Path value in the manifest.

The source of the issue seems to be that Knot does not look into classpath jars' manifests to identify the full classpath and instead just looks at the java.class.path property.

Relevant location in Knot