Bug 123786 Following bug 109980, the compliance 6.0 should be added to the compiler's compliance list.
If the JRE/JDK used is a 1.6/6.0 VM, then the compliance 6.0 should be available. Compliance 1.6 implies source level 1.6 and target level 1.6.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/ComplianceConfigurationBlock.java
status.setError(PreferencesMessages.ComplianceConfigurationBlock_src14tgt14_error); 
				return status;
			}
		} else if (VERSION_1_5.equals(source)) {
			if (!VERSION_1_5.equals(target)) {
				status.setError(PreferencesMessages.ComplianceConfigurationBlock_src15tgt15_error); 
				return status;
			}
		}
		return status;
	}
	
	
	/* (non-Javadoc)
	 * @see org.eclipse.jdt.internal.ui.preferences.OptionsConfigurationBlock#useProjectSpecificSettings(boolean)
	 */
	public void useProjectSpecificSettings(boolean enable) {
		super.useProjectSpecificSettings(enable);
		validateJRE50Status();
	}
		
	/*
	 * Update the compliance controls' enable state
	 */		
	private void updateComplianceEnableState() {
		boolean enabled= checkValue(INTR_DEFAULT_COMPLIANCE, USER_CONF);
		for (int i= fComplianceControls.size() - 1; i >= 0; i--) {
			Control curr= (Control) fComplianceControls.get(i);
			curr.setEnabled(enabled);
		}