dictextension dict

Fix a bug where selecting a server that never responds
to the DICT commands put the preferences into a bad state.

Compute nsIPrefBranch once and save it in DictExtension

Use the new name of DictExtension.getDefaultServerDatabaseName()

Style the preferences dialog box

Add code to notify the user when their preferred database is not on the server.
Also fix a problem where "Search All Databases" would become unselected when the databases were found.

Add storePreferenceToField, a helper for writing a preference to a hidden field in the DOM.

Simplify the callback parameter for getting the list of databases.
There's no need to create a class of objects to receive the callbacks.
A simple object is sufficient.

Fix a UI annoyance where, if the user selected a server-specific
database, the database would be set to 'Search All Dictionaries'
until the response from 'SHOW DB' returned.

In order to show what the user previously selected, we now store
both the database name (the part that DICT cares about) and the
human-readable database description.

Fix two mistakes made in the previous revision
1) Only select a database if the host/port match the default
2) Remove the now-defunct updateSupportedDatabases

Inline updateSupportedDatabases into its only caller.
This simplies to overall code and removes some code duplication.