Change package_db collection of packages from vector to a map so we can look things...

Change package_db collection of packages from vector to a map so we can look things up in it quickly

This allows packagedb::findBinary() and packagedb::findSource() to be re-written to locate packages
by name rather than searching the entire set, which makes a big difference to total execution time.

        * IniDBBuilderPackage.cc (IniDBBuilderPackage): Remove db.packages vector
        sorting.
        (buildPackage, buildPackageSource): Change package collection from vector
        to map.
        * PickView.cc (setViewMode, init_headers, defaultTrust): Ditto.
        * choose.cc (createListview, logResults, keepClicked)
        (changeTrust): Ditto
        * install.cc (do_install_thread): Ditto
        * download.cc (do_download_thread): Ditto
        * prereq.cc (isMet): Ditto
        * package_meta.cc (ScanDownloadedFiles): Ditto
        * package_db.h (packagedb): Ditto
        * package_db.cc (packagedb, flush, markUnVisited, setExistence)
        (fillMissingCategory): Ditto
        (findBinary, findSource): Rewrite to locate packages in map rather than
        searching the whole vector, for performance.
        (ConnectedLoopFinder, doIt, visit): Rewrite to refer to package using a
        packagemeta *, as an index into the vector of packages can no longer be
        used.