Copy all fields of the am_opts structure

Copy all fields of the am_opts structure

When we introduced am_loc we also added a function to create a
duplicate of an am_opts structure. As it turns out, that only made
a partial copy of the struct and some fields (e.g. opt_cache) was
left blank in the new structure.

Unfortunately any code that was checking the options through the
mntfs structure was mislead by the partial copy: caching was disabled
completely, for example, and since browsing relies on caching being
enabled it wasn't working either.

From: Krisztian Kovacs <Kris.Kovacs@morganstanley.com>