Equal PersistentOrderedSets are not equal

[FerrumBrain]

In the following example we have two indentical sets that aren’t equal from assertEquals perspective:

val set1 = persistentSetOf(-486539264, 16777216, 0, 67108864)
val builder = set1.builder()

assertEquals(set1, builder)
assertEquals(set1, builder.build())
assertEquals(set1, builder.build().toSet())


val set2 = set1.remove(0)
builder.remove(0)

assertEquals(set2, builder.build().toSet())
assertEquals(set2, builder.build()) // fails, expected to pass

Bug is found by fuzzing team @ PLAN Lab.

[I-Iege]

maybe this is also related to
#198

[fzhinkin]

It seems to be the same issue as #198, which is indeed reproducible starting from 0.3.5 where optimized equals implementations where introduced: ec42c96#diff-73b47fb05e3a34a7f620efdf8c6dcbde78f72cdfc8f6ed532da314c6bc93a0e1

The problem here, apparently, is that value removal might result in a different trie structure (at least, after #73) and optimized equals compares nodes for exact equality.