* src/stash.c: switch from saving a path and removing the file to a
    	push/pop interface, allowing multiple ccaches and ticket files to
    	exist at the same time
    * src/v4.c,src/v5.c: use push/pop to create/remove files
    * src/tokens.c: use the topmost ccache name
    * src/session.c: don't skip creating ccache/ticket files when we've
    	already done so