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/internal/ui/jarpackager/JarFileExportOperation.java
private void buildProjects(IProgressMonitor progressMonitor) {
		Set builtProjects= new HashSet(10);
		Object[] elements= fJarPackage.getElements();
		for (int i= 0; i < elements.length; i++) {
			IProject project= null;
			Object element= elements[i];
			if (element instanceof IResource)
				project= ((IResource)element).getProject();
			else if (element instanceof IJavaElement)
				project= ((IJavaElement)element).getJavaProject().getProject();
			if (project != null && !builtProjects.contains(project)) {
				try {
					project.build(IncrementalProjectBuilder.INCREMENTAL_BUILD, progressMonitor);
				} catch (CoreException ex) {
					String message= JarPackagerMessages.getFormattedString("JarFileExportOperation.errorDuringProjectBuild", project.getFullPath()); 
					addError(message, ex);
				} finally {
					
					builtProjects.add(project);
				}
			}
		}
	}
	/**
	 * Tells whether the given resource (or its children) have compile errors.
	 * The method acts on the current build state and does not recompile.
	 * 
	 * @param resource the resource to check for errors
	 * @return <code>true</code> if the resource (and its children) are error free
	 * @throws import org.eclipse.core.runtime.CoreException if there's a marker problem