Support setting local variables through info items

[ralphlange]

The % redirection parameter often breaks the layering, as record names are required within the protocol file.

Redirection targets can be set through protocol parameters, but - especially for protocols that return a whole bunch of values - this can make database links completely unreadable.

Idea: Allow setting local StreamDevice variables (scope: protocol) through info items. A record in the database could do something like

    info(stream:varLINK1, "myotherrecord.A")
    info(stream:varSTATUS, "mystatusrecord")

and the protocol could

    out "VAL?";
    in "%("$LINK1")f,%("$STATUS")i";

Advantage: all record names stay in the database; the protocol file can use redirections and still be application agnostic.

I am willing to work on this, if we can agree on the general idea and interface.