handle invalid arguments

[egandunning]

Running Exporter.py with invalid arguments resulted in the following error message:

$ python Exporter.py --whoops
Traceback (most recent call last):
File "Exporter.py", line 79, in <module>
main(sys.argv[1:])
File "Exporter.py", line 75, in main
outputFile.close()
UnboundLocalError: local variable 'outputFile' referenced before assignment

I moved all file io into a with block, and removed the finally block. This way, if getopt() throws an exception, the program won't call close() on an uninitialized variable.

Running the same command now gives the following output:

$ python Exporter.py --whoops
Arguments parser error, try -h

option --whoops not recognized