Bug 29755 Attach source does not allow one to select a folder... [build path]
When opening some .class that does not yet have a source attachment eclipse shows a text version of the interface defintion and a button for Attaching source. When pressing this button a window appaer where one can enter the name/location of a folder, zip or jar for the source. There are also a button for choosing it via a file selection dialog and this works fine for zip and jar files - but not for selecting a directory :( Workaround is just to enter the directory manually.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
*/
	private IPath modifyPath(IPath path, String varName) {
		if (varName == null || path == null) {
			return null;
		}
		if (path.isEmpty()) {
			return new Path(varName);
		}
		
		IPath varPath= JavaCore.getClasspathVariable(varName);
		if (varPath != null) {
			if (varPath.isPrefixOf(path)) {
				path= path.removeFirstSegments(varPath.segmentCount());
			} else {
				path= new Path(path.lastSegment());
			}
		} else {
			path= new Path(path.lastSegment());
		}
		return new Path(varName).append(path);
	}
	/**
	 * Creates a runnable that sets the source attachment by modifying the project's classpath.
	 * @deprecated use getRunnable() instead
	 */
	public IRunnableWithProgress getRunnable(final IJavaProject jproject, final Shell shell) {
		fProject= jproject;
		return getRunnable(shell);
	}
	/**