Have iconv accept redundant escape sequences in IBM900, IBM903, IBM905,

IBM907, and IBM909.

Patch for bug #17197 changes the encoder to avoid generating redundant
shift sequences.  However, those sequences may already be present in
data encododed by prior versions of the encoder.  This change modifies
the decoder to also avoid rejecting redundant shift sequences.

        [BZ #19432]
        * iconvdata/Makefile: Add bug-iconv11.
        * iconvdata/bug-iconv11.c: New test.
        * iconvdata/ibm930.c: Do not reject redundant shift sequences.
        * iconvdata/ibm933.c: Same.
        * iconvdata/ibm935.c: Same.
        * iconvdata/ibm937.c: Same.
        * iconvdata/ibm939.c: Same.