qt: add proxy to options overridden if necessary.

If proxy is disabled in the gui but enabled via the command line, it needs to
be added to the override list.
Abstract out SignatureChecker
Make signature cache optional
Replace SCRIPT_VERIFY_NOCACHE by flag directly to checker
Don't translate state.Abort() messages

There is only one message passed to AbortNode() that makes sense to
translate to the user specifically: Disk space is low. For the others
show a generic message and refer to debug.log for details.

Reduces the number of confusing jargon translation messages.
Update English translation
Make comptool more deterministic
travis: add non-default shell testing to travis.
Bugfix: Replace bashisms with standard sh to fix build on non-BASH systems
Bugfix: Replace bashisms with standard sh in gitian descriptors
Bugfix: Replace bashisms with standard sh in tests/tools
Merge pull request #5035

c9c51cb Make comptool more deterministic (Matt Corallo)
Disable App Nap on OSX 10.9+
Merge pull request #4890

e790c37 Replace SCRIPT_VERIFY_NOCACHE by flag directly to checker (Pieter Wuille)
5c1e798 Make signature cache optional (Pieter Wuille)
c7829ea Abstract out SignatureChecker (Pieter Wuille)
Merge pull request #5036

eb6b3b2 Update English translation (Wladimir J. van der Laan)
b9b2e3f Don't translate state.Abort() messages (Wladimir J. van der Laan)
minor license, header end comment etc. cleanup in /script

- ensure all licenses are just MIT
- add a missing header end comment
- ensure alphabetical ordering
fix a lock indentation in main.cpp

- also ensure alphabetical ordering in file header
minor txindex documentation improvement
Homebrew lang fix

Very small tweak to correct the language on Homebrew's sandboxing process.

Discussed in [this commit](https://github.com/bitcoin/bitcoin/commit/9fedafba4b903d7f3af044eb86dc313856e40b08).
Merge pull request #5049

4dc5eb0 fix a lock indentation in main.cpp (Philip Kaufmann)
5eed8c2 minor license, header end comment etc. cleanup in /script (Philip Kaufmann)