Bug 9159 Classpath wizard should not complain when adding missing source folder
Build 20020125 - Define a project A with source folder 'src1'. - Go to the .classpath file and edit it to insert one extra line: <classpathentry kind="src" path="src2"/> below the line referring to first source folder: <classpathentry kind="src" path="src1"/>. - Now, try to add this missing source folder 'src2', it isn't allowed by the wizard, one has to add a basic folder instead. Note: It is not such an uncommon scenario, the classpath modification could simply occur by catching up with a shared classpath having one more source folder on it, and which is locally missing.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/BuildPathsBlock.java
if (currElement.getEntryKind() == IClasspathEntry.CPE_SOURCE) {
				if (!isChecked) {
					fClassPathList.setCheckedWithoutUpdate(currElement, true);
				}
			} else {
				currElement.setExported(isChecked);
			}
			entries[i]= currElement.getClasspathEntry();
			entryMissing= entryMissing || currElement.isMissing();			
		}
				
		if (entryMissing) {
			fClassPathStatus.setWarning(NewWizardMessages.getString("BuildPathsBlock.warning.EntryMissing")); 
		}
				
		if (fCurrJProject.hasClasspathCycle(entries)) {
			fClassPathStatus.setWarning(NewWizardMessages.getString("BuildPathsBlock.warning.CycleInClassPath")); 
		}	
	}
	/**
	 * Validates output location & build path.
	 */	
	private void updateBuildPathStatus() {
		fOutputLocationPath= null;
		
		String text= fBuildPathDialogField.getText();
		if ("".equals(text)) { 
			fBuildPathStatus.setError(NewWizardMessages.getString("BuildPathsBlock.error.EnterBuildPath")); 
			return;
		}