Resampling should be more accurate

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Using a box filter should only read every channel value once for. But
there exist some cases where the value if read 0 or 2 times.
This may improve the quality of the scaling slightly.

Original issue reported on code.google.com by m%[email protected] on 23 Aug 2009 at 8:49

[GoogleCodeExporter]

See testcase 7 for more details.

Original comment by m%[email protected] on 23 Aug 2009 at 8:51