installer: establish a stable registry key for the location and installer options

[dscho]

This will be helpful for add-on tools, possibly add-on localization, too.

[dscho]

In particular, there needs to be a standardized way to look up the directory where to install additional helpers, such as credential and remote helpers.

[kjeremy]

Should the keys go under HKCU instead if installed for the local user?

[dscho]

@mikofski ummm.... wrong ticket????

[dscho]

@mikofski a little research would be nice: it is not even far away, it is the third most recent updated (and already fixed!) issue: #455

[mikofski]

@dscho so sorry about that. comment nixed. :)

[dscho]

@mikofski that's not what I asked... I asked to comment on the correct ticket. @kjeremy also commented here by mistake, but then went on to open that new ticket, and things were resolved. The trick about mistakes is not to hide them, but to learn from them...