series of improvement

grat: file reading going outside site loop

improved deciding of calling new alias file to open

close nc files before opening new one for new date
this cased crushes when two many file was opened
see file usage with lsof -p $(ps -ax |grep grat |grep -v grep)

improved calling for file with alias opening

now there is no unnecessary nf90_open call
only if really date change and opening of new file is wanted