Command line only needs '<,'> for command mode

Search mode doesn't need it, so it is better to move this to the
CommandLineParser code.
Fix searchmode's hint handling; exception handling
Pass FROM_VISUAL hint if searching in visual modes

The selection must be stored so that search mode can work correctly. The
FROM_VISUAL hint will make sure that this happens.

Fixes #500.
Add tests for repeated search mode (normal/visual)

Also see issue #500.