Fix deduplication for post hooks

[presidento]

The problem was that if both a and b tasks have same pre and post hooks, the a b was extended and deduplicated to pre a post b. But the post hook means that it must be run after the original task.

With this commit there are 3 rules of deduplication:

• don't touch direct task calls (a a b must remain the same)
• keep only the first of the same pre-hooked tasks (pre a pre b becomes pre a b)
• keep only the last of the same post-hooked tasks (a post b post becomes a b post)

Fixes #298

[codecov-io]

Current coverage is 93.23%

Merging #299 into master will increase coverage by +0.03% as of 25368ef

@@            master    #299   diff @@
======================================
  Files           20      20       
  Stmts         1722    1730     +8
  Branches       298     300     +2
  Methods          0       0       
======================================
+ Hit           1605    1613     +8
  Partial         31      31       
  Missed          86      86       

Review entire Coverage Diff as of 25368ef

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[bitprophet]

Thanks. At this time, I do agree with the overall intent here (re: pushing post-hooked dependencies to the last spot possible). Need to scan the actual diff harder but adding to a release milestone.

[presidento]

I am happy to fix if you don't think the current implementation is not fit to the actual conception. (We would like to use this functionality.)

[mnagy]

Hello, any news? I'd really love to see this fixed.