FilterToSQL: try converting to Number before converting to String
CompareFilterImpl: Handle case where both values are strings that can be cast to numbers
FilterToSQL: try converting to Number before converting to String

CompareFilterImpl: Handle case where both values are strings that can be cast to numbers
Undo change to SLDStyleFactoryTest
Some additional tests for comparing numbers/strings
Merge pull request #324 from mbertrand/numberfix_master

Fix some issues with SQL filtering and comparison