Various changes to make this script work on Linux/\*BSD systems

- Linux/\*BSD `date` command lacks the `-v` flag, but has an equivalent construct, `-d "X days ago"` (set using the `OSXDATE` flag)
- Linux/\*BSD `mysqld` requires a change to the server config, and use of the `--local-infile=1` flag to `mysql` (set using the `REQUIRES_LOCAL_INFILE` flag)
- added configurable `LOGDIR` to set where the logfile is stored (since most Linux/\*BSD boxen lack `$HOME/Library/Logs`)
- updated README with these new configurable options
- additionally updated README to note that this script works fine with "sales-only" iTC users; those leery of using their primary iTC user/password can create a "sales-only" sub-account with a different password and use that instead.