PasswordType: use RAW impl for Oracle instead of non-existent VARBINARY

If I'm not mistaken, the Oracle SQL DB (at least 11g R2) doesn't have a VARBINARY type.
This fix uses a RAW (binary) type instead for the Oracle dialect.
Re-added missing impl attribute
Merge pull request #82 from mkai/patch-1

PasswordType: use RAW impl for Oracle instead of non-existent VARBINARY