Log Message:
libass: update to 0.13.4

changes from 0.13.1 to 0.13.4

    Bug fixes found with fuzzing
    Fix memory reallocation in the shaper. (CVE-2016-7972)
    Fix two small memory leaks in the parser and test program.
    Fix illegal read in Gaussian blur coefficient calculations. (CVE-2016-7970)
    Fix mode 0/3 line wrapping equalization in specific cases which could result \ 
in illegal reads while laying out and shaping text. (CVE-2016-7969)

    Improve compatibility/portablility of build system, should fix e.g. \ 
compilation on Solaris.
    Fix memory leak in DirectWrite font provider.
    Fix the rasterizer when rendering some large outlines.
    Remove hack that forced RTL base direction depending on font encoding.
    Greatly improve the internal caches with refcounting and gradual clearing.

    Add ass_set_check_readorder() API function to disable use of the ReadOrder \ 
field for duplicate checking in ass_process_chunk().
    ass_step_sub(track, now, 0) now finds the start of the subtitle at now.
    Bug fixes:
        Fix an issue with the new duplicate checking, which could lead to \ 
missing subtitles after seeking.
        Fix a crash with Core Text under specific circumstances.