Ability to specify actual database type when bind parameter to a query

[tarasko]

From backends_smoke_test.cpp

// Oracle require explicit specification which type we going to bind: BLOB or CLOB, 
// istreams in oracle backend are always bound as BLOBs, that is why you can`t bind to anything except blob columns 
// in database. Actually the same problem we have with odbc drivers that don`t support SQLDescribeParam. 
// Fortunally MSSQL driver support it.

edba try to guess database type specifically in each backend and in most time it is done very well, but that`s not enought. Frontend should allow user to specify which database type has parameter during binding. Possible syntax:

st << use("name", value, dbt_blob);
st.bind("name", value, dbt_clob);