BENCH syntax support and tests for various minor bugs and changes

I implemented draft support for an inline benchmark syntax extension,
pa_bench (BENCH, etc.), that we are using internally.  It's analogous
to the inline unit test syntax extension, pa_ounit (TEST, etc.).
(pa_bench will be included in a future public release of Core.)

I also implemented draft support for more monadic operators we are
using.  I believe these come from outside.

I added tests for a number of minor bugs and tweaks, including the
default record field value syntax we apparently use.

(ocp-indent has been released internally at Jane Street as the default
indenter for all developers.  Some of these tests are results.)

Thanks!