secp256k1: add libtool as a dependency
secp256k1: Add build-side changes for libsecp256k1

Note: This is added to our existing automake targets rather than as a
libtool-style lib. The switch to libtool-style targets can come later if it
proves to not add any complications.
libsecp256k1 integration
Clean up release-process.md after OS X gitian changes

This is PR #4271, but with the changes to the descriptors, both the names of the
files and the names of the intermediate build artifact archives, removed.
This also closes #3775 if it goes in, because it covers the changes in
that PR.
Fix the Qt5 build after d95ba75

Sorry, my own fault this time.
Merge pull request #4449

462ad22 Clean up release-process.md after OS X gitian changes (Micha)
Merge pull request #4312

fda3fed libsecp256k1 integration (Pieter Wuille)
5566826 secp256k1: Add build-side changes for libsecp256k1 (Cory Fields)
b150b09 secp256k1: add libtool as a dependency (Cory Fields)
qt: fix 'opens in testnet mode when presented with a BIP-72 link with no fallback'

Passes tests:

```
$ ./bitcoin-qt 'bitcoin:?r=http://www.example.com/'
.. fixed the original problem - this launches mainnet.

$ ./bitcoin-qt 'bitcoin:mngeNQbTKnmaMbx8EXCYdwUbnt9JJD52cC'
.. launches testnet

$ ./bitcoin-qt -testnet 'bitcoin:1NXXeQRyMFFFRfyUix2o7mk1vhvk2Nxp78'
.. sanity check - launches mainnet.
```

Fixes #4355. Closes #4411.