File behaviour

What's the expected behaviour of the file settings?

Goals, in order

1. Act exactly like PuTTY if there are no file settings, until the user asks for files.
2. Don't read or write the registry if there are file settings, unless the user asks for registry.
3. Have some logical behaviour for Default Settings.

Creating a portable config

1. Create a empty putty.conf file next to putty.exe
2. For "Default Settings" and each of the settings you might already have in the "Sessions from Registry" tab:
   • "Load" it, then change over to "Sessions from file" tab and "Save".
   • "Delete" it from the "Sessions from registry" tab.
3. Delete the HKEY_CURRENT_USER\Software\SimonTatham\PuTTY registry key for good measure.
4. Now all the settings will be saved in the PuTTY directory which you can take anywhere with you, and PuTTy will open to the "Sessions from file" tab by default, and registry will be untouched from now on.

See #49 for more details.

Primitives

1. Do we have any registry settings?
2. Do we have any file settings?
3. Do we have Default Settings in the registry?
4. Do we have Default Settings in files?

..

when reg, and file is selected {
  mode -> file
  load defaults
}

and v.v.?