Fixed the problem with segfaults - actually a bug/limitation in

Fixed the problem with segfaults - actually a bug/limitation in
Linux mmap(2) - mmap was placing the new segment just before
libc with only a tiny bit of headroom, so when the file grew
by gigabytes, it trashed libc and other vital libraries.  Allow
the base address to be specified to get around this.

Don't override standard malloc/free.  Not sure if this makes any
difference, but I'd prefer mmalloc to do its own thing.

Test program now imports whole of Perrys logfiles.