Bridge: Rename method getByPk() to getByKey()
Bridge: Fix param error of execute with parpare for sybase db

In the SQL, $table is used multiple times, so prepared execute need a value
array as input data. For simple, removed prepare, the raw execute without
prepare should not cost much more.
Bridge: Avoid use MetaPrimaryKey() in ADOdb for sybase ase

In sybase not ase this may have problem, but seems not much people are using
sybase now.
Bridge: Replace method GetRowAssoc() with FetchRow()

In ADOdb manual, GetRowAssoc() should not use with $ADODB_FETCH_MODE =
ADODB_FETCH_ASSOC. When use sybase it product an error message:

    Undefined offset: 0

So replace it will FetchRow(), works fine now.
Auth: Add method getIdentity()
Auth: Avoid duplicate start session