Fixed calculation of unfiltered PDF

1. I think there was some error associated with using the file handle 23 for opening and closing the PDF files. I changed it to 88.
2. The viz.xy file was being opened one more time than necessary. Otherwise the code looks good.
Finally fixed the unfiltered pdf

I was getting negative pdfs. Although it seemed to work for analysis of less than 10 time steps.
1. real(5000*768*768) gives a negative number because of overflow
2. dble(5000*768*768) gives a negative number because of overflow
3. dble(dble(5000)*dble(768)*dble(768)) seems to work
Merge branch 'fixUnfilteredPDF' into calcPDF