Error handling

[pyhedgehog]

Preface

Command bt open $(bt windows|sed -ne '$ s/\t.*$//p') <<<https://www.google.com/ correctly opens tab with google search page.
Command bt open $(bt windows|sed -ne '$ s/\t.*$//p') <<<https://www.buggydomain.com/ opens with error reporting invalid address. And this is correct result too.

Bug demo

1. Run bt open $(bt windows|sed -ne '$ s/\t.*$//p') <<<about:config if you are using Firefox, else choose some of browser-specific privileged urls^*.
2. You'll see TimeoutError that is bad enough already.
3. Run some bt command, i.e. just bt windows.
4. You'll got empty output because bt_mediator is dead. To recover you should disable/enable plugin in about:plugins.

Expected results

1. Bug report output from bt open command.
2. No server death.