Real-time output file name fix

[egthomas]

This pull request slightly modifies the behavior of rtcfit, rtgrid, and rtsnd by allowing the user to set the radar name used for the real-time output files via an optional -name command line option.

By default, the three-letter station name is taken from the radar parameter block of the real-time data stream. However, sometimes that value can become corrupted / invalid, causing the stid to be set to zero and the files to be labeled as belonging to the tst radar.

[egthomas]

and apologies to @ecbland - I promise this is the last fix I try to add to the 5.0 release!

[ecbland]

This compiles ok. Merging now

[egthomas]

Thanks @ecbland!