change validation to use ValidationContext, nest contexts when entering a Subquery fixes #1943120 and paves the way for subquery validation
change validation to use ValidationContext, nest contexts when entering a Subquery fixes #1943120 and paves the way for subquery validation

git-svn-id: d7f6d3fc66399c4a8ff072a18ddf9297da8786ca@197 f9ba57bc-9804-47c6-9de9-2f2ff8aac994

jahlborn/sqlbuilder,jahlborn/sqlbuilder