AGOS: Archive code cleanup

This pull requests removes ArchiveMan from AGOS and replaces it with Common::File/SearchMan. This makes the code more consistent (there were still bits using Common::File before too) and also cleaner/smaller.

As a side effect this "fixes" bug 6506: http://sourceforge.net/p/scummvm/bugs/6506/ because Common::File has the workaround for filenames with a trailing dot in place.

I only tried starting up Simon 1 DOS/CD, Simon 1 Amiga CD32, Simon 2 DOS/CD, The Feeble Files Amiga. Those seem to work fine. It would be good if someone with The Feeble Files with a CAB archive could test this before we merge this.