[Proj] Gridshifts give slightly wrong results

[Uwe Schmitz]

Hello,

I've upgraded from proj-4.4.7 to 4.5.0 and
notice a slight difference of my transformation
results when grid shifts are involved. 

Executing the command:
cs2cs -f "%.12f" \
      +proj=latlong +ellps=bessel +nadgrids=./BETA2007.gsb \
   +to \
      +proj=latlong +ellps=GRS80
7.483333333333E 53.500000000000N

results in 
7.482506019176  53.498461143331 0.000000000000   # 4.4.7 correct!
7.482506019176  53.498461144236 0.000067942776   # 4.5.0

Through debugging I found out, that now (V4.5.0) there
is an additional step converting the geodetic coordinates
to geocentric an back again. This is caused by the different
ellipsoids.

IMO, this is a bug, because the datum shift is completely
done by adding the shift values.

Regards
Uwe