[System.Data.SqlClient] Support for "Connection Lifetime" parameter

Adding support for "Connection Lifetime" parameter in connection strings.
This is especially fundamental in this scenario:
- Pooling is ON because the app is in constant reception of requests.
- Loadbalancer is switched to point to a new database.
- Mono needs to discard the connections that are too old (marked by lifetime)
in order to create new ones, that will connect to the new DB.

It includes a unit test in Mono.Data.Tds testing assembly.

Patch contributed under the terms by the X11/MIT license, by:
 James Lewis <james.lewis@7digital.com>
 Andres G. Aragoneses <andres@7digital.com>
[System.Data.SqlClient] Use DEFAULT_CONNECTIONLIFETIME const in the code

We had created the constant for the pull request but we were not actually
using it, oops!
[Mono.Data.Tds] Add Obsolete constructors to unbreak the API

As Miguel points out, this assembly could be used by other people outside
Mono, so let's not break the API and make these constructors pass a 0
default connection lifetime (in this case the connection lives forever as
it used to happen before bringing connection lifetime support).
Merge pull request #1 from knocte/master

Unbreak API and other nitpicks
Merge pull request #517 from getsometoast/master

[System.Data.SqlClient] Support for "Connection Lifetime" parameter