undup-fuse: fix integer overflow with 2GB bucket

debug output with a 3.3 GiB undup.dat:

[1363129438.609] lookup got 1 4 -760848384
[1363129438.609] pread(4, 0x14045b0, 7, -760848384)

Following the code, `off' is off_t but its assigned value is
computed in 32 bits because all of the constituent values are 32 bits:

    *off = HASH_BLOCK * (1 + j + (i * (1 + nhash)));

Simplest fix is to tag HASH_BLOCK as long long.
undup-fuse: remove extra cast of HASH_BLOCK

with previous commit making HASH_BLOCK a LL, no need to cast
to off_t in the one place I'd noticed to do that properly.
undup-fuse: debug bucket_validate and fixup false-positive statistics
undup-debug: fixup format arg size problems
undup-core: remove dump_blooms during every insert
cflags: -Wno-unused-parameter to reduce noise
add pthread_rwlock to threadsafe-ify bucket access
undup-core: query bloom1 correctly with bp1, not bloom0