Backport r523 into the stable branch.

Improve the message error handling by mimicking the behavior of the info/report logs.

Output the error messages to the standart error message until the context is correctly initialized. Then, output the error messages to a file if the user has set "print_file" parameter to "true".

  - Fix: Errors that occured before MPI was initialized (e.g. during the config file parsing) caused a MPI error on top of the original error.
 - Fix: The error file could sometimes be misnamed if the error happened before the context was completely known.

git-svn-id: http://forge.ipsl.jussieu.fr/ioserver/svn/XIOS/branchs/xios-1.0@548 d613d254-d18a-4304-b296-5125d4c4d670