modify the test_be suite so that offsets are tested

[simsong]

Most of the tests in test_be put the object to be found at an offset of 0. However, most of the scanners now special-case looking at each offset so that they do not incur the cost of creating new sbufs. Therefore the test program needs to be updated so that besides testing each scanner with the target at 0 offset, it also tries at, say, 65 byte offset (so that it also checks for non 4-byte, not-packing alignment).