Add some host key dialogue boxes. These still look a little rough around

Add some host key dialogue boxes.  These still look a little rough around
the edges and need to have all their controls properly aligned and spaced
according to the HI guidelines.  Also, fix store_host_key() so that it
replaces a host key correctly when the host key has changed and the user
opts to update the cached one.

[originally from svn r5280]