Convert fuse.c to C++.

Fix string literals and cast void* appropriately. Alternatively, we
could switch some of the allocations to new/delete, but we would need
to make sure that none of those end up passed to other code that will
call free(3) on them.

Bug: 30110940
Change-Id: I6f39df65cd960930530e5a1f8420a28d50adc25d