* replacing calls to not-always-available gmtime_r with our own code.
     The new helper function actually differs in semantics from gmtime_r,
     so if that seems to be a problem I can actually move it to dv.c
     completely, since only DV muxer uses the code anyway.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@3399 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b