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
if (pkgFragment != null)
							pkgRoot= JavaModelUtil.getPackageFragmentRoot(pkgFragment);
						else
							pkgRoot= findPackageFragmentRoot(jProject, resource.getFullPath().removeLastSegments(1));
					} catch (JavaModelException ex) {
						addWarning(JarPackagerMessages.getFormattedString("JarFileExportOperation.javaPackageNotDeterminable", resource.getFullPath()), ex); 
						return;
					}
				}
			}
			
			if (pkgRoot != null) {
				leadSegmentsToRemove= pkgRoot.getPath().segmentCount();
				boolean isOnBuildPath;
				isOnBuildPath= jProject.isOnClasspath(resource);
				if (!isOnBuildPath || (mustUseSourceFolderHierarchy() && !pkgRoot.getElementName().equals(IPackageFragmentRoot.DEFAULT_PACKAGEROOT_PATH)))
					leadSegmentsToRemove--;
			}
			
			IPath destinationPath= resource.getFullPath().removeFirstSegments(leadSegmentsToRemove);
			
			boolean isInOutputFolder= false;
			if (isInJavaProject) {
				try {
					isInOutputFolder= jProject.getOutputLocation().isPrefixOf(resource.getFullPath());
				} catch (JavaModelException ex) {
					isInOutputFolder= false;
				}
			}