Converts an IRS 990 e-file XML URL into a standardized OBJECTID
(prefixed with OID-) used as a database key.
Details
The ID is taken from the file name (<OBJECTID>_public.xml), so
any host or folder works: GTDC XmlFiles/, NCCS xml/, and the patch
folders under xml2/ (e.g. xml2/v2_3_patch/). Earlier versions removed a
fixed list of URL prefixes, so a URL from any other folder produced a key
that still contained the URL.