Fix assertion failure in circuit.merkle_tree_gadget_weirdness test on Windows
zcash-gtest.exe fails
```
[ RUN ] circuit.merkle_tree_gadget_weirdness
Assertion failed!
Program: C:\zcash-gtest.exe
File: ./snark/libsnark/gadgetlib1/gadgets/basic_gadgets.tcc, Line 50
Expression: this->pb.lc_val(packed).as_bigint().num_bits() <= bits.size()
```
The argument type of `__builtin_clzl()` function is unsigned long.
So, we need to replace `__builtin_clzl` with `__builtin_clzll`. (The argument type of `__builtin_clzll()` is unsigned long long (64bit)).
Refactor ContextualCheckBlock tests
This cleans up and condenses our quadratically-scaling transaction format / consensus rule tests. They still technically scale quadratically, but should be much more readable and manageable now - all that remains in the individual test cases is the specific version flag tweaking we're trying to test.
Closes#3187.
Use ZIP 32 for all Sapling spending keys
The wallet now only stores Sapling extended spending keys, and thus can
only be used with keys generated from an HDSeed via ZIP 32. This means
that all Sapling keys and addresses generated by users can be recovered
as long as they have a backup that includes the seed.
Depends on zcash/librustzcash#29
Closes#3380.
Jack Grigg