osx: fix signing to make Gatekeeper happy (again)

The approach from 65f3fa8d1 worked for signing on 10.9.4, but not newer
versions. 10.9.5 (and up) want each framework to stand alone.

Now in addition to copying the plist's from Qt for each framework, we put them
in per-version dirs and only symlink to the latest, rather than using symlinks
for any contents.
Fix formatting in  init.md
tests: fix python test-runner for windows

Windows needed a few fixups to get the tests running:
1. bitcoin-tx needs a file extension in Windows. Take this opportunity to
   add an env file, which pulls variables out of our build config. This can
   be extended as needed, for now it's very simple.
2. After #1, split the args out of the exec key in the test data.
3. Correct the line-endings from windows stdout
Update build-unix.md

Debian also need libboost-all-dev installed.
Merge pull request #5014

41d67c7 tests: fix python test-runner for windows (Cory Fields)
Merge pull request #5018

347a3a3 Update build-unix.md (JL2035)
Merge pull request #5005

af0bd5e osx: fix signing to make Gatekeeper happy (again) (Cory Fields)
Merge pull request #5008

41020eb Fix formatting in  init.md (Whit J)