Feature: added support for collecting popup (confirm/alert/prompt) messages
and providing default value for different Javascript popups.

1. All the different popup messages collected in popup_messages list.
2. You can pass default value to use for confirm/alert/prompt dialogs, without
the need to use the with statement (in case you just want the popup to go away).
3. Little refactoring to GhostWebPage: I'm passing the Ghost object to it,
so we won't need to use global variables. This refacotring can later be applied
to _alert and similar variables.
Merge pull request #77 from EverythingMe/feature_collect_prompt_messages

Feature: added support for collecting popup (confirm/alert/prompt) messages and default value
Merge pull request #82 from EverythingMe/fix_hash_header

Fix: Support for URLs with hashes that are sent to server.
Convert popup message to unicode rather than str.
Make sure the result value in GhostWebPage.javaScriptPrompt is always string (otherwise error occurs).
Only set Ghost._prompt_expected/_confirm_expected if default_popup_response is not None.
Do not clear Ghost._confirm_expected/_prompt_expected (it gets cleared anyway by the with statement).
Resolve merge conflicts