[pgjdbc/pgjdbc] befea1: Add SCRAM-SHA-256 support (#842)

Branch: refs/heads/master
Home: https://github.com/pgjdbc/pgjdbc
Commit: befea18d153dda7814daef4e036d3f5daf8de1e5
https://github.com/pgjdbc/pgjdbc/commit/befea18d153dda7814daef4e036d3f5daf8de1e5
Author: Álvaro Hernández Tortosa <aht(at)8kdata(dot)com>
Date: 2017-11-21 (Tue, 21 Nov 2017)

Changed paths:
M .travis.yml
M pgjdbc/pom.xml
M pgjdbc/src/main/java/org/postgresql/core/v3/ConnectionFactoryImpl.java
A pgjdbc/src/main/java/org/postgresql/jre8/sasl/ScramAuthenticator.java

Log Message:
-----------
Add SCRAM-SHA-256 support (#842)

* Add SCRAM-SHA-256 support

PostgreSQL 10 comes with SCRAM-SHA-256 support. This commit introduces
support for it.

Work is based on an external dependency, the SCRAM client library:

https://github.com/ongres/scram/

which is now imported as a dependency.

TODO:
- SCRAM client library will be improved, on its own.
Particularly, StringPrep support needs to be added. Final
version of pgjdbc will depend on v1.0
- Testing
- Probably macros to avoid this Java8-only code propagating to
Java < 8 versions of the driver

* Prepare Java8-only code to be excluded for jre<=8

Actually implemented via macros by JDBC < 4.2.

* On HEAD all testing connections will use SCRAM

* Better error message for drivers w/o SCRAM support

* added configuration for shaded jar
remove any extraneous classes picked up in the shade plugin