Linux script fix at exit viewer.
Allow switching between HTTP and UDP inventory without relogging.

This also makes the viewer immune for grids that send the FetchInventory2 et al
capabilities regardsless of whether we requested them (in fact, we always
request them now: we need them when someone switches in the middle of a session).

Note that (I tested that) textures could already be switched between
HTTP and UDP without relogging.