In scope of SQL/session services WLs a fix for sending decimal over binary
protocol was introduced.  The fix turned out to be incomplete and led to a
wrong result of type_decimal test in the ps-protocol mode.  It's caused by
insufficient format information given to the protocol - only number's
precision
is provided, while field's precision is also needed.

Now Protocol::store_decimal() accepts two more arguments - precision and
decimals. Protocol_text and Protcol_binary are using them to correctly send
data. Those new args aren't exported to plugins via callbacks in
Protocol_callback as this info is already available in query's metadata.

No need in a new test as type_decimal is indicative enough.