Failure recovery

[Thorium]

I have a (quite common scenario I suppose) web server using SQLProvider to connect a database that is located on a different server.

Sometimes the network connection does fail. That is the nature of HTTP. I try to deal with that having a retry logics when calling GetDataContext().

Now, if the web-server runs a maintenance boot (Windows update) and the network connection is not up and running when the server restarts, this is what happens:

• Server will start, but the connection is in a broken state
• If the connection is stored to a static variable, all the queries will crash on runtime even when the connection has been restored. Maybe because the column dictionary is empty or something.
• This can be fixed by accessing the connection as a function, having a backing-field for the connection, and creating it again if it's null.
• Another problem seems to be that if the server is running for long time, it seems that the primary-key dictionary goes to empty. This will cause update clauses not to work. I don't know yet the scenario and why but I think it's again about network connection breakups.

Besides that, there is more generic infrastructure, described more detailed in #238 but that started to be off-topic so I started a new issue.

Should we have some kind of extra-functions-namespace (like namespace FSharp.Data.Sql.Extensions) in SQLProvider to provide customers some tools to fight with this kind of nasty real life problems?