mdiff: fix diff -b/B/w on mixed whitespace hunks (issue127) Previous code was computing hunks then checking if these hunks could be ignored when taking whitespace/blank-lines options in accounts. This approach is simple but fails with hunks containing both whitespace and non-whitespace changes, the whole hunk is emitted while it can be mostly made of whitespace. The new version normalize the whitespaces before hunk generation, and test for blank-lines afterwards.