fork()/exec()/waitpid() error handling in Grip

Hi,

Recently Debian unstable had a problem with the libFLAC library so oggenc
didn't work at all:

$ oggenc
oggenc: error while loading shared libraries: libFLAC.so.6: cannot open
shared object file: No such file or directory
$ echo $? 
127

I was using Grip to convert a couple of CD to .ogg at that time
and everything seemed to work: Grip ripped the .wav's and supposedly
encoded them too. Of course the .ogg's were missing due to this FLAC
issue, but Grip showed no error signs even though oggenc returned an
error and even the Status tab showed nothing about the error.

The attached patch to grip-3.2.0 from Debian unstable works better when
the encoder fails but it totally sucks in normal succesfull case - there
must be better ways of doing this.

I think there should be a generic way of checking how spawned processes
exit'ed in Grip:

- Perhaps every fork/exec should be followed by a waitpid() to check that
the return value is ok, but that make's the UI sluggish as the main
process is blocking all the time. 

- A sigaction() approach seems more complicated if every spawned process
needs to be tracked, but perhaps it could be used to track all spawned
processes as a bunch and for example cancel the encoding if any of the
encoding processes fail. I think Grip should tell the user if for
example disk fills up during encoding or ripping, at least in the Status
tab.

What do you think?

I'm no *nix programming expert, but I could perhaps scratch my itch :)

-Mikko


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