Add spelling suggestions for four cases:

Add spelling suggestions for four cases:

1. For targets, when invoking ninja to build a target.
2. For targets, when doing a "query" command.
3. For command names.
4. For the subcommands of the "targets" command.

Also change CmdTargets() to call LookupNode() instead of GetNode() --
since the result was checked for NULL, that's probably what was intended
here originally.