non-integer COUNTS column

Steve Snowden ran into a silent problem because he made spectrum files with non-integer COUNTS columns. This is in violation of the standard and many ftools will simply silently truncate the float value to the nearest integer. I've added checks in the low-level library routines to write warnings in this case.

Update on 5/7/09. It turns out that the RXTE s/w writes PHA files with a real COUNTS column although the values are integers. So, I've improved the checking so that no warnings are given if the values are integers even if the column is defined as real. If the values really are non-integer then a warning is written and the values truncated to integers.