Bug 63840 warning on unused labels
we have warnings for all sorts of unused things. one for unused labels would be good too.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/ProblemSeveritiesConfigurationBlock.java
private static final Key PREF_PB_HIDDEN_CATCH_BLOCK= getJDTCoreKey(JavaCore.COMPILER_PB_HIDDEN_CATCH_BLOCK);
	private static final Key PREF_PB_UNUSED_LOCAL= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_LOCAL);
	private static final Key PREF_PB_UNUSED_PARAMETER= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_PARAMETER);
	private static final Key PREF_PB_SIGNAL_PARAMETER_IN_OVERRIDING= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_PARAMETER_WHEN_OVERRIDING_CONCRETE);
	private static final Key PREF_PB_SIGNAL_PARAMETER_IN_ABSTRACT= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_PARAMETER_WHEN_IMPLEMENTING_ABSTRACT);
	private static final Key PREF_PB_SYNTHETIC_ACCESS_EMULATION= getJDTCoreKey(JavaCore.COMPILER_PB_SYNTHETIC_ACCESS_EMULATION);
	private static final Key PREF_PB_NON_EXTERNALIZED_STRINGS= getJDTCoreKey(JavaCore.COMPILER_PB_NON_NLS_STRING_LITERAL);
	private static final Key PREF_PB_UNUSED_IMPORT= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_IMPORT);
	private static final Key PREF_PB_UNUSED_PRIVATE= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_PRIVATE_MEMBER);
	private static final Key PREF_PB_STATIC_ACCESS_RECEIVER= getJDTCoreKey(JavaCore.COMPILER_PB_STATIC_ACCESS_RECEIVER);
	private static final Key PREF_PB_NO_EFFECT_ASSIGNMENT= getJDTCoreKey(JavaCore.COMPILER_PB_NO_EFFECT_ASSIGNMENT);
	private static final Key PREF_PB_CHAR_ARRAY_IN_CONCAT= getJDTCoreKey(JavaCore.COMPILER_PB_CHAR_ARRAY_IN_STRING_CONCATENATION);
	private static final Key PREF_PB_POSSIBLE_ACCIDENTAL_BOOLEAN_ASSIGNMENT= getJDTCoreKey(JavaCore.COMPILER_PB_POSSIBLE_ACCIDENTAL_BOOLEAN_ASSIGNMENT);
	private static final Key PREF_PB_LOCAL_VARIABLE_HIDING= getJDTCoreKey(JavaCore.COMPILER_PB_LOCAL_VARIABLE_HIDING);
	private static final Key PREF_PB_FIELD_HIDING= getJDTCoreKey(JavaCore.COMPILER_PB_FIELD_HIDING);
	private static final Key PREF_PB_SPECIAL_PARAMETER_HIDING_FIELD= getJDTCoreKey(JavaCore.COMPILER_PB_SPECIAL_PARAMETER_HIDING_FIELD);
	private static final Key PREF_PB_INDIRECT_STATIC_ACCESS= getJDTCoreKey(JavaCore.COMPILER_PB_INDIRECT_STATIC_ACCESS);
	private static final Key PREF_PB_EMPTY_STATEMENT= getJDTCoreKey(JavaCore.COMPILER_PB_EMPTY_STATEMENT);
	private static final Key PREF_PB_UNNECESSARY_ELSE= getJDTCoreKey(JavaCore.COMPILER_PB_UNNECESSARY_ELSE);
	private static final Key PREF_PB_UNNECESSARY_TYPE_CHECK= getJDTCoreKey(JavaCore.COMPILER_PB_UNNECESSARY_TYPE_CHECK);
	private static final Key PREF_PB_INCOMPATIBLE_INTERFACE_METHOD= getJDTCoreKey(JavaCore.COMPILER_PB_INCOMPATIBLE_NON_INHERITED_INTERFACE_METHOD);
	private static final Key PREF_PB_UNUSED_DECLARED_THROWN_EXCEPTION= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_DECLARED_THROWN_EXCEPTION);
	private static final Key PREF_PB_MISSING_SERIAL_VERSION= getJDTCoreKey(JavaCore.COMPILER_PB_MISSING_SERIAL_VERSION);
	private static final Key PREF_PB_UNDOCUMENTED_EMPTY_BLOCK= getJDTCoreKey(JavaCore.COMPILER_PB_UNDOCUMENTED_EMPTY_BLOCK);
	private static final Key PREF_PB_FINALLY_BLOCK_NOT_COMPLETING= getJDTCoreKey(JavaCore.COMPILER_PB_FINALLY_BLOCK_NOT_COMPLETING);
	private static final Key PREF_PB_UNUSED_DECLARED_THROWN_EXCEPTION_WHEN_OVERRIDING= getJDTCoreKey(JavaCore.COMPILER_PB_UNUSED_DECLARED_THROWN_EXCEPTION_WHEN_OVERRIDING);
	private static final Key PREF_PB_UNQUALIFIED_FIELD_ACCESS= getJDTCoreKey(JavaCore.COMPILER_PB_UNQUALIFIED_FIELD_ACCESS);
	private static final Key PREF_PB_MISSING_DEPRECATED_ANNOTATION= getJDTCoreKey(JavaCore.COMPILER_PB_MISSING_DEPRECATED_ANNOTATION);
	private static final Key PREF_PB_FORBIDDEN_REFERENCE= getJDTCoreKey(JavaCore.COMPILER_PB_FORBIDDEN_REFERENCE);
	private static final Key PREF_PB_DISCOURRAGED_REFERENCE= getJDTCoreKey(JavaCore.COMPILER_PB_DISCOURAGED_REFERENCE);