Panic if page provided to freelist.read is incorrect page type.

[jpbetz]

Encountered this when debugging an issue found by etcd-io/etcd#8813 CI tests.

This check simply aims to fail fast if ever bolt attempts to load a non-freelist page as a freelist, which has the potential to lead to data corruption.

[codecov-io]

Codecov Report

Merging #66 into master will decrease coverage by 0.09%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master      #66     +/-   ##
=========================================
- Coverage   85.56%   85.47%   -0.1%     
=========================================
  Files           9        9             
  Lines        1857     1859      +2     
=========================================
  Hits         1589     1589             
- Misses        159      160      +1     
- Partials      109      110      +1

Impacted Files	Coverage Δ
freelist.go	81.7% <0%> (-1.01%)	⬇️

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[gyuho]

For compatibility with all etcd 3.2.* releases, the NoFreelistSync option introduced in #1 will not be enabled.

So, we never saw this in etcd because we always set NoFreelistSync: true?

[jpbetz]

Yes, still hunting down root cause of the etcd-io/etcd#8813 CI failure, but it appears to be a bug with freelist writes that only applies when NoFreelistSync: false, which we don't test on master because we have NoFreelistSync: true there.

[xiang90]

lgtm