Added negative scan increment compatibility

And moved duplicated loopwise incrementing line

fuerte backport (cherry picked from commit 1bb7353deff061dc0e5b0b0ea477b1e5fa370668)
Better solution of negative increment compatibility.

The previous commit assumes a laser_filter configuration with lower_angle > upper_angle, which wouldn't be inter robot compatible. Now lower_angle is expected to be smaller than upper_angle even if the increment is negative.
Word fix in comments: rays, not scans
Merge pull request #2 from felix-kolbe/fuerte_patch

Added negative scan increment compatibility