1<<30 bytes of memory, which is required for some streams.
Also, try to make the taster more discriminating about raw lzma streams.
The detection here is still really weak, though; please use xz instead
of lzma.
Since FreeBSD doesn't have liblzma in the base system, the
read side will always fall back to the unxz/unlzma commands for now.
(Which will in turn fail if those commands are not currently
installed.) The write side does not yet have a fallback, so
that will just fail.
