r.colors: fix order of rules

[metzm]

When applying scale and/or offset to r.colors, color rules were written out in reverse order. This PR fixes the ordering of color rules.

GRASS itself has no problems with a reverse order of color rules, but r.colors.out and subsequent r.colors.out_sld create broken output.

[metzm]

How to test in the NC sample dataset:

g.region raster=elev_state_500m
g.copy rast=elev_state_500m,my_elev_state_500m
# no scale, all fine
r.colors map=my_elev_state_500m color=srtm_plus
r.colors.out_sld map=my_elev_state_500m
# scale, should not have reverse ordering
r.colors map=my_elev_state_500m color=srtm_plus scale=0.5
r.colors.out_sld map=my_elev_state_500m

[neteler]

Thanks, the example works fine.

[metzm]

TODO: backport 150a0e9

[neteler]

TODO: backport 150a0e9

done!