Bug 37197 Basepath for relative pathes in JAR-exporter
The basepath for the JAR-exporter is the eclipse-install-directory. I prefer it to be the root of the project (the description is saved in), so that relative pathes end inside the project. Now: <jardesc> <jar path="workspace/projectdir/jar.jar"/> Desired: <jardesc> <jar path="jar.jar"/> Reason: To make the jardesc-files portable for shared projects
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/jarpackager/JarWriter.java
private JarOutputStream fJarOutputStream;
	private JarPackageData fJarPackage;
	
	/**
	 * Creates an instance which is used to create a JAR based
	 * on the given JarPackage.
	 *
	 * @param jarPackage		the JAR specification
	 * @param parent			the shell used to display question dialogs,
	 *				 			or <code>null</code> if "false/no/cancel" is the answer
	 * 							and no dialog should be shown
	 * @throws	CoreException	to signal any other unusal termination.
	 * 								This can also be used to return information
	 * 								in the status object.
	 */
	public JarWriter(JarPackageData jarPackage, Shell parent) throws CoreException {
		Assert.isNotNull(jarPackage, "The JAR specification is null"); 
		fJarPackage= jarPackage;
		Assert.isTrue(fJarPackage.isValid(), "The JAR package specification is invalid"); 
		if (!canCreateJar(parent))
			throw new OperationCanceledException();
		try {
			if (fJarPackage.usesManifest() && fJarPackage.areClassFilesExported()) {
				Manifest manifest=  fJarPackage.getManifestProvider().create(fJarPackage);