merge-base master 2.9.1

Fix for SI-4929. Includes (previously failing) test case.

This uses thread-local variables, which is not ideal; however, I can't
find any way to fix it otherwise that doesn't involve significant
refactoring.

Version number: 2.8.2.RC3 -> 2.8.2.final

Version number change assuming RC4 will be the ...

Version number change assuming RC4 will be the final, which may or may
not be true.

Scala 2.9.1 RC3 -> RC4

RC2 -> RC3

2.9.1 RC1 -> RC2

Selective reversions, mostly over improbable bi...

Selective reversions, mostly over improbable binary compatibility
issues.

Temporary version change: 2.9.1.alpha -> 2.9.0.1

RC5 -> final