lib/Automake/File.pm: Modifie file_contents_internal

lib/Automake/File.pm: Modifie file_contents_internal

This function now takes a list of paragraph as argument instead of building it
in its code.  This is the first step in the modification of this function to
be able to test it with files that don't "physically" exist in the actual file
system.

* lib/Automake/File.pm: Start the modification of file_contents_internal for
  unit testing