fix php errs, improve bitcache_admin_bitstream_fetch_validate()

Hi there,
testing this there was an error coming up because of only two pipes being requested but three assigned in bitcache.inc... then there was another issue where i couldn't fetch a file with an obscure file name via the fetch tab, so i implemented some code which i think now can cope with any url given.. During debugging that i also discovered that the default prefix and language entries in the options array given to l() are being set in there already so i removed those.
One question that has arisen trying out the fileframework module: shouldn't bitcache save at least the original file name? surely identifying bitstreams by some checksum is the right way to deal with it, but file names do provide some additional usability. Especially when fetching from somewhere else, recording that original name surely could be of help?