Prevent 'db.view' function from modifying provided query options object.

[dmitrymatveev]

db.view function modifies the passed-in options object which may lead to unexpected behaviour.

One case is when client code is using a reference to the same view options objects multiple times to query a view. This results in query options object differ from its original state yielding incorrect couchDB url string on consecutive calls to db.view function.

// E.g: stringifying params.key multiple times
var params = { key : 123 }
async.timesSeries( 5, function ( n, cb ) {
        db.view( 'design/view', params, function () { cb();});
}, function () {
        // params now equals to : {key: ""\"\\\"\\\\\\\"123\\\\\\\"\\\"\"""} 
});

[dmitrymatveev]

apparently this is a fix for pull request #239 (how did I not see that when going over those just ten minutes ago)