Catch more exceptions thrown from IO in TopLevel

[atomb]

As part of fixing #678 (in PR #1194), I adapted the io function in SAWScript.Value to explicitly handle a couple of exception types. This might be a good place to consolidate handling of exceptions we expect may be thrown by IO code. Doing so might be as simple as changing a bunch of liftIO calls in TopLevel functions to io and extending the list of exceptions we have explicit handlers for.

[sauclovian-g]

SAW code should not throw random exceptions from I/O; it should use the upcoming uniform SAW error apparatus. So this should be limited to things we expect to arrive from elsewhere.

Also note that these days that io is the same as liftIO.