Add Visual Studio 2012 solution file
Fix VersionLoader column selector

Fix VersionLoader to find the Version column by name so that it will not
matter if there are extra columns or the columns are not ordered as expected.
Make versionless migrate respect existing DB version

Previously, running the migrate without specifying a version would apply
all migrations in the supplied assembly without regard to the database's
current version. Now, it will use the highest version in the assembly as
the target, causing it to skip all migrations that have already been applied.