support classpath specified inside manifest

[akozlova]

As by javadoc of java.util.jar.Attributes.Name#CLASS_PATH
/**
* Name object for Class-Path
* manifest attribute. Bundled extensions can use this attribute
* to find other JAR files containing needed classes.
* @see
* JAR file specification
*/
This way it would be possible to compact long classpaths (on win) without introduction of artificial classloader.

Inspired by https://youtrack.jetbrains.com/issue/IDEA-149275

[edwardsa]

This issue completely prevents cpsuite being usable in IntelliJ 15 when you have a long classpath. This is because in IntelliJ 15 they switched to use manifest classpaths.