Allows support of comment in udta for libquicktime, also currently \251des is used
 which is ignored by mov.c.
\251cmt IS currently already picked up by mov.c

References

libquicktime
http://libquicktime.cvs.sourceforge.net/viewvc/libquicktime/libquicktime/src/udta.c?view=markup

Also listed here:
http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/QuickTime.html#UserData

Not listed here, but that`s not entirely surprising, as udta fields are expected to be somewhat arbitary.
http://developer.apple.com/library/mac/#documentation/QuickTime/qtff/QTFFChap2/qtff2.html#//apple_ref/doc/uid/TP40000939-CH204-BBCCFFGDSigned-off-by: Michael Niedermayer <michaelni@gmx.at>