Respect schema data type in constraint validation

This patch makes Constraint objects aware of the data type of the
owning Schema object so constraint validation can apply potential
type casts based on the data type.
This is especially useful and necessary for an AllowedValues
constraint and numeric values, where items may be defined as
strings or numbers and cause comparison issues with user values
at runtime.

Change-Id: Id1884b4968993fc9356e7ba4ad03dced4cd00d4e
Closes-Bug: #1321540
Merge "Respect schema data type in constraint validation"