Relax the block count check on deallocation in env_test

It seems that on some FS we get more blocks than we ask for. This is
already handled when checking the allocated number of blocks, but
after the file is closed it checks for an exact number of blocks,
which fails on my machine.

I changed the test to add one full page to the size, then calculate
the expected number of blocks and check if the actual number of blocks
is less or equal to that.
Merge pull request #395 from lalinsky/fix-env-test

Relax the block count check on deallocation in env_test
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