Improve rednoise behaviour when writing output files

[alex88ridolfi]

rednoise now always writes the _red.fft and _red.inf files in the same directory (previously it would write the _red.fft file in the current working directory, and the _red.inf file in the directory specified in the "Data file name without suffix" entry of the original *.inf file)

Also, if the directory specified in the original *.inf file does not exist, rednoise now writes the output files in the current working directory (previously it would crash).

Finally, it now prints the paths of the output files, similarly to other PRESTO routines.

[alex88ridolfi]

I should have implemented the suggested changes. Please have a look and let me know if it looks fine to you.