FieldCalculations are not correctly calculated for the grand total
rows and columns. They have to be calculated using the
FieldCalculation-function, as a sum of a percentage value is wrong.

I.e. old behavior:
           Value1   Value2  %(Value1 of Value2)
A          20       30      66,66
B          50       56      89,28
GrandTotal 70       86      155,94

This is just wrong.

Fixed behavior:
           Value1   Value2  %(Value1 of Value2)
A          20       30      66,66
B          50       56      89,28
GrandTotal 70       86      81,39
Merge pull request #14 from rototor/field_calculation_grandtotal_fix

FieldCalculations are not correctly calculated for the grand total