Bug fix: tmp dir not existing so radars.sqlite can't be downloaded.

Fixed an error with the temp dir not existing which prevents the radars sqlite file from being updated.

To test this bug fix, 
1) Delete your DAVIT_TMPDIR and then start davitpy. You will receive an error that says: 
"sqlInit() Error unable to open database file: /tmp/sd/.radars.sqlite"
This is a __big__ problem because plotting and file reading depends on radars.sqlite being available.
2) From the command line, create your DAVIT_TMPDIR and then restart davitpy, this time you will see a message that says: "Radars information has been updated."
3) Delete your DAVIT_TMPDIR, install this bug fix, and then start davitpy. You won't receive the sqlInit() error.
4) Rejoice!