Make table checkout/checkin case-insensitive #56

The checkout system can get into an unrecoverable state if a table name with any capitalization other than the lower-case name of the table in postgres is checked out (e.g. Master in place of master). When this happens:

• The table is still marked as exported, but
• The export has no data, and
• Attempted check-in with any capitalization fails

The arguments to run.py should be case insensitive to the extent possible. The solution in this case is to apply string.lower() to the table name when arguments are parsed in run.py