Add -Wl,-pie linker option for macOS and use it instead of -pie
fixes linker error (see below) due to "-pie" usage, replaced it with "-Wl,-pie" for macOS platform
```
clang: error: argument unused during compilation: '-pie' [-Werror,-Wunused-command-line-argument]
```
Update README.md
Added default options to build zcash with as many parallel compilation units as there are cpu cores.
This makes compiling zcash multiple times faster.
Fix absurd fee bug reported in #3281, with tests
This was ported from the Hush `absurd_fee_bug` PR: https://github.com/MyHush/hush/pull/136
Tests executed with `./qa/pull-tester/rpc-tests.sh wallet` and pass on Ubuntu 16.04. Some tests were added for previously untested behavior as well.
Closes#3281.
Add change indicator
This adds to the json returned when calling z_listreceivedbyaddress and z_listuspent an additional field entitiled 'change' which will be either true or false depending on whether or not the note was change from another transaction.
Extend JoinSplit tests to Groth
As we now have both PGHR and Groth proofs for Sprout - make the joinsplit tests check the Groth proofs as well.
See https://github.com/zcash/zcash/issues/3266
(rpc-test) accurately account for fee without rounding error
Fix for #2807, this test compares balances after doing key exports and imports, and expects these balances to be equal. But they are not exactly equal due to transaction fees, so the test makes them "equal" by rounding a value that has had fees taken out up to the nearest hundredth of a unit (which is much more than the default fee). This obviously is somewhat sloppy. It also converts a balance to float, which really should never be used due to loss of precision (use Decimal instead).
This change makes the test accurately account for the fee using precise comparisons, and removes the use of float. This test doesn't depend on the default fee (0.0001) but instead sets the fee (to that value). This way, if the default fee changes in the future, this test will continue to run. While testing these changes, I set the fee to various values (up to the max, 0.0190), and the test still passes.
Closes#3328. Send alert to put non-Overwinter nodes into safe mode.
The alert targets nodes running protocol version <= 170004.
Overwinter compatible nodes run protocol version >= 170005.
