configure.ac: bump gettext version

configure.ac: bump gettext version

Version 1.19.1 was released in June 2014.

    configure.ac:697: warning: AM_PROG_MKDIR_P: this macro is deprecated, and will soon be removed.
    configure.ac:697: You should use the Autoconf-provided 'AC_PROG_MKDIR_P' macro instead,
    configure.ac:697: and use '$(MKDIR_P)' instead of '$(mkdir_p)'in your Makefile.am files.
    ./lib/autoconf/general.m4:2434: AC_DIAGNOSE is expanded from...
    aclocal.m4:780: AM_PROG_MKDIR_P is expanded from...
    m4/po.m4:23: AM_PO_SUBDIRS is expanded from...
    m4/gettext.m4:57: AM_GNU_GETTEXT is expanded from...
    configure.ac:697: the top level
    configure.ac:697: warning: The macro `AC_TRY_LINK' is obsolete.
    configure.ac:697: You should run autoupdate.
    ./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...
    lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    ./lib/autoconf/general.m4:2249: AC_CACHE_VAL is expanded from...
    ./lib/autoconf/general.m4:2270: AC_CACHE_CHECK is expanded from...
    m4/gettext.m4:365: gt_INTL_MACOSX is expanded from...
    m4/gettext.m4:57: AM_GNU_GETTEXT is expanded from...
    configure.ac:697: the top level
    configure.ac:697: warning: The macro `AC_TRY_LINK' is obsolete.
    configure.ac:697: You should run autoupdate.
    ./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...
    lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    ./lib/autoconf/general.m4:2249: AC_CACHE_VAL is expanded from...
    ./lib/autoconf/general.m4:2270: AC_CACHE_CHECK is expanded from...
    m4/gettext.m4:57: AM_GNU_GETTEXT is expanded from...
    configure.ac:697: the top level
    configure.ac:697: warning: The macro `AC_TRY_LINK' is obsolete.
    configure.ac:697: You should run autoupdate.
    ./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...
    lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    ./lib/autoconf/general.m4:2249: AC_CACHE_VAL is expanded from...
    ./lib/autoconf/general.m4:2270: AC_CACHE_CHECK is expanded from...
    m4/iconv.m4:20: AM_ICONV_LINK is expanded from...
    m4/gettext.m4:57: AM_GNU_GETTEXT is expanded from...
    configure.ac:697: the top level