Memory: Eliminate use of HasFlag

[bgrainger]

The Visual Studio .NET Memory Allocation profiler shows columnDefinition.ColumnFlags.HasFlag(ColumnFlags.Unsigned) (in MySqlDataReader) as allocating a 4-byte ColumnFlags object. The equivalent bitwise test (columnDefinition.ColumnFlags & ColumnFlags.Unsigned) != 0 has no allocations.

Replace Enum.HasFlag with the equivalent bitwise test in any code that might be called frequently during data access.

(Wait for #136 since it'll be rearranging a lot of the usages of HasFlag.)

[bgrainger]

Fixed in 0.7.1.