Mapping errors due to already-existing file, but no duplicate ids in batch

[kspurgin]

Record id "CC2004.52.1f.001" mapped fine, and written to: Q0MyMDA0LjUyLjFmLjAwMQ==.xml

Subsequent record id "CC2004.52.1L.001" maps ok, but fails to write XML file, with error:

An XML record with filename Q0MyMDA0LjUyLjFMLjAwMQ==.xml has already been written. Check for duplicates.

Compare:

Q0MyMDA0LjUyLjFmLjAwMQ==.xml
Q0MyMDA0LjUyLjFMLjAwMQ==.xml
---------------^------------

The filenames produced by CMT::Xml::FileNamer are unique, but the filesystem ignores case differences. Hooray for being "helpful," MacOS.

Options for this:

• Ignore it. It happens fairly rarely and only in gigantic batches (so far). Run the error row from the orig batch as a subsequent fixup batch after the initial batch is done.
• Create a case-sensitive disk partition and move all data work to that (not likely for me any time soon, but remember this when you get a new laptop!)
• Update CMT to add some qualifier to the file name if the File.exist? check in CMT::Xml::FileWriter returns true. S3 keys are case sensitive, and the S3 key creation does not depend on the file name. Thanks, past-me.