makes sure getDisplayPrecision is properly get/set from ConceptNumeric to ConceptFormBackingObject

+ adds testcase
Merge pull request #524 from openmrs-codejam-hamburg/TRUNK-3903

TRUNK-3903: makes sure getDisplayPrecision is properly get/set from ConceptNumeric t...
Unable to invoke getForms after adding FormField to
containingAnyFormField - TRUNK-4189