Fix input_fps option type for count_seqs.py

Fixes item `count_seqs.py` of issue #632.

`count_seqs.py` accepts UNIX-style wildcards for paths. This has resulted in a change in the option_parsing.py library, allowing all the scripts with the option type `input_filepaths` to accept these wildcards.

It is a bit hackish because this option type have to preserve the order in which the paths has been given. This is needed by scripts such `merge_otu_maps.py`, where the order of the files matters.