[Libburn] Patch to enable arbitrary input fd (updated 2nd submission)

[scdbackup at gmx.net]

Hi,

meanwhile i remembered the motivation for 
burn_source_get_size() :

Fixed size shall be orthogonal to any kind of data
source.

If one would interpret the fixed size within
burn_source.get_size(), then each such function would
have to take the fixed size into respect.

My proposal to transfer the functionality into
file_size() would indeed implement that for the
only .get_size() which i can spot for now.
So far that would be ok.

But is it desirable ?
Isn't a wrapper around the specialized .get_size()
functions the better way to enforce the application's
will to burn exactly the given amount of bytes ?

We could allow with
  burn_fd_source_new(fd,size)
the size to be 0 so that the .get_size() functions
can be used even with that constructor. 
I made it refuse 0 in order to achieve more safety
against misunderstandings. With stdin currently 
0 is not senseful. 
But if there will ever be a write mode which does not
need to know the source size in advance, 0 might be
exactly the right setting. 

Ok. I will have to adapt my patch proposal anyway.
I will then remove the size-0-restriction from it.
(So it is able to burn empty CDs. Interesting feature.)


Have a nice day :)

Thomas