Speed up equivalence comparisons

[viluon]

~~This PR improves performance on all the five benchmarks (and hopefully in real life too)~~. It does so simply by taking some shortcuts when the left and right operands of eq, le, and lt point to the same object.

Disregard the above. I need to verify that this change has any (positive) performance impact at all. The previous benchmarks were not representative.

[SquidDev]

On master:

# Run complete. Total time: 00:23:40

PerformanceBenchmark.binarytrees  thrpt   15  3.977 ? 0.137  ops/s
PerformanceBenchmark.fannkuch     thrpt   15  5.974 ? 0.225  ops/s
PerformanceBenchmark.nbody        thrpt   15  0.599 ? 0.024  ops/s
PerformanceBenchmark.nsieve       thrpt   15  0.289 ? 0.018  ops/s

On feature/fast-equiv:

# Run complete. Total time: 00:23:15

Benchmark                          Mode  Cnt  Score   Error  Units
PerformanceBenchmark.binarytrees  thrpt   15  4.051 ? 0.180  ops/s
PerformanceBenchmark.fannkuch     thrpt   15  6.187 ? 0.309  ops/s
PerformanceBenchmark.nbody        thrpt   15  0.718 ? 0.016  ops/s
PerformanceBenchmark.nsieve       thrpt   15  0.300 ? 0.012  ops/s

This does end up being slightly faster. Couple of other changes it may be worth trying if I've a little more time:

• Reverting the changes to toDouble. Shouldn't really have any impact on performance, but we should see.
• Only applying this patch in the case of eq.