fixup! fixup! fixup! fixup! fixup! ZBigFile: Add ZBlk format option 'h' (heuristic) (4)

This patch improves the test which compares the performance of the
different ZBlk formats by using test data which better represents the
behaviour of a real-world instance that actually uses 'wendelin.core'
with the 'many-small-appends' use-case.

---

Running 'bigfile/tests/test-zblk-fmt' with improved test data results
in:

Run append tests
---------------------------------------------
---------------------------------------------
Set change_percentage_set to 0.014
Set change_count to 500
Set arrsize to 500000
Set change_type to append

Run tests with format auto:

	ZODB storage size: 29.428379 MB
	Access time: 0.785 ms / blk  (initially cold; might get warmer during benchmark)

Run tests with format ZBlk0:

	ZODB storage size: 538.109848 MB
	Access time: 0.754 ms / blk  (initially cold; might get warmer during benchmark)

Run tests with format ZBlk1:

	ZODB storage size: 16.844756 MB
	Access time: 88.665 ms / blk  (initially cold; might get warmer during benchmark)

---------------------------------------------
---------------------------------------------

bigfile/tests/test-zblk-fmt

@@ -70,7 +70,7 @@ function test {
 
 
 echo "Run append tests"
-test 0.15 500 500000 "append"
+test 0.014 500 500000 "append"
 
 # TODO(add 'small changes after initial fillup' optimization, see
 # 'bigfile/file_zodb/ZBigFile_zblk_fmt_heuristic' for more details)