containing an error code.

Allow these functions to convey the reason of the failure to the
calling function, failure which is not always due to a parsing error
but it may depend for example on a memory problem.

Also fix several potential memleaks.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@23402 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b