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/JarPackageData.java
*/
	public IFile getDescriptionFile() {
		IPath path= getDescriptionLocation();
		if (path.isValidPath(path.toString()) && path.segmentCount() >= 2)
			return JavaPlugin.getWorkspace().getRoot().getFile(path);
		else
			return null;
	}	
	
	/**
	 * Gets the manifest's main class.
	 * 
	 * @return	the type which contains the main class or,
	 * 			<code>null</code> if none is specified
	 */
	public IType getManifestMainClass() {
		return fManifestMainClass;
	}
	/**
	 * Set the manifest's main class.
	 * 
	 * @param mainClass the type with the main class for the manifest file
	 */
	public void setManifestMainClass(IType manifestMainClass) {
		fManifestMainClass= manifestMainClass;
	}
	/**
	 * Returns the elements which will be exported.
	 * These elements are leaf objects e.g. <code>IFile</code>
	 * and not containers.