Input routines
load a file in gzip format
load a file in bzip format - Not implemented yet
load a non compressed file
load a file either in gzip, bzip or not compressed format
parse a uri. i.e. : deb://path/to/file rpm://path/to/file cudf://path/to/file
guess the input format from a list of list of uris and check if the list is omogenueous w.r.t the guessed format. Fails otherwise