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
addToStatus(ex);
			}
			progressMonitor.done();
		}
	}
	
	protected boolean preconditionsOK() {
		if (!fJarPackage.areClassFilesExported() && !fJarPackage.areJavaFilesExported()) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.noExportTypeChosen"), null); 
			return false;
		}
		if (fJarPackage.getElements() == null || fJarPackage.getElements().length == 0) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.noResourcesSelected"), null); 
			return false;
		}
		if (fJarPackage.getJarLocation() == null) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.invalidJarLocation"), null); 
			return false;
		}
		File targetFile= fJarPackage.getJarLocation().toFile();
		if (targetFile.exists() && !targetFile.canWrite()) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.jarFileExistsAndNotWritable"), null); 
			return false;
		}
		if (!fJarPackage.isManifestAccessible()) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.manifestDoesNotExist"), null); 
			return false;
		}
		if (!fJarPackage.isMainClassValid(new BusyIndicatorRunnableContext())) {
			addError(JarPackagerMessages.getString("JarFileExportOperation.invalidMainClass"), null);