Missing Poco::DynamicAnyHolderImpl<Data::BLOB>::value() method added

To use BLOB together with DynamicAny
SQLite INT to Poco::Int64

SQLite INTEGER column can have according to documentation up to 64 bits.
Then I suppose it should be by default stored to Int64.
Merge pull request #299 from hadzim/poco-1.4.6

Missing Poco::DynamicAnyHolderImpl<Data::BLOB>::value() method added