Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (c *Collection) RemoveAll(selector interface{}) (info *ChangeInfo, err error) {
	lerr, err := c.writeQuery(&deleteOp{c.FullName, selector, 0})
	if err == nil && lerr != nil {
		info = &ChangeInfo{Removed: lerr.N}
	}
	return info, err
}
func (c *Collection) RemoveAll(selector interface{}) (info *ChangeInfo, err error) {
	lerr, err := c.writeQuery(&deleteOp{c.FullName, selector, 0})
	if err == nil && lerr != nil {
		info = &ChangeInfo{Removed: lerr.N}
	}
	return info, err
}
// RemoveAll finds all documents matching the provided selector document
// and removes them from the database.  In case the session is in safe mode
// (see the SetSafe method) and an error happens when attempting the change,
// the returned error will be of type *LastError.
//
// Relevant documentation:
//
//     http://www.mongodb.org/display/DOCS/Removing
//