Add the Int32 type to rpc-light.

Note that the autogen code never generates this, it's purely
intended for places where for whatever reason you really need to
marshal an int32 into an xmlrpc <i4> tag.

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #18 from jonludlam/rpc-light-int32

Add the Int32 type to rpc-light.