parallelize test runner on non-Linux platforms

parallelize test runner on non-Linux platforms

Closes #903

Differential Revision: D904203
Normalize spelling of "prologue"

We had both "prologue" and "prolog" all over the place, and it was
starting to drive me nuts. I picked "prologue" because it seems to be
the more standard spelling. Both are valid in American English, but in
the rest of the English-speaking world, only "prologue" is standard.

Differential Revision: D904232
Log status of all curl requests during test

Use exec("curl ...") instead of the curl API to make server requests, so that every interaction with the server can be traced and logged.

Differential Revision: D902614
Remove a bunch of separable extensions cruft

This code hasn't been relevant in a long time.

Differential Revision: D904562
Implement PHP_BINDIR (core constant)

Implement PHP_BINDIR PHP core predefined constant. PHPUnit (via PEAR) uses this constant in its self-test suite, causing many of them to fail on HHVM (possibly only because of the lack of this constant). Try to ninitially implement in such a way that it can be nimble enough for open-source, cross platform.

Differential Revision: D900077
remove dead option from docs

remove MaxStackDepth from docs, not used/implemented
remove unimplemented memcache-related statistics/settings

Closes #911

Differential Revision: D904848