duplicate_definition for internal classes with throwing constructors

[parzysty]

For following lime file
`
package smoke

open class ExternalClass {
enum ErrorEnum {
NONE,
CRASHED
}

class InternalOne {
    @Dart(Default)
    constructor create() throws ConstructorExploded   
}

class InternalTwo {
    @Dart(Default)
    constructor create() throws ConstructorExploded   
}

exception ConstructorExploded(ErrorEnum)

}
`

generated dart code contains multiple declaration of

final _$initReturnReleaseHandle = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Void Function(Pointer<Void>),
    void Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalOne_create_return_release_handle'));

final _$initReturnGetResult = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Pointer<Void> Function(Pointer<Void>),
    Pointer<Void> Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalOne_create_return_get_result'));

final _$initReturnGetError = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Uint32 Function(Pointer<Void>),
    int Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalOne_create_return_get_error'));

final _$initReturnHasError = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Uint8 Function(Pointer<Void>),
    int Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalOne_create_return_has_error'));

and

final _$initReturnReleaseHandle = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Void Function(Pointer<Void>),
    void Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalTwo_create_return_release_handle'));

final _$initReturnGetResult = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Pointer<Void> Function(Pointer<Void>),
    Pointer<Void> Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalTwo_create_return_get_result'));

final _$initReturnGetError = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Uint32 Function(Pointer<Void>),
    int Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalTwo_create_return_get_error'));

final _$initReturnHasError = __lib.catchArgumentError(() => __lib.nativeLibrary.lookupFunction<
    Uint8 Function(Pointer<Void>),
    int Function(Pointer<Void>)
  >('library_smoke_ExternalClass_InternalTwo_create_return_has_error'));

which fail to compile