Bug-fix missing parallel support.

[linas]

The CMakefile calls this HAVE_PARALLEL_ALGORITHM not HAVE_PARALLEL_STL

[linas]

@ngeiswei -- please take a look.

With stdc++17, I think pretty much everything you want is in std, and so OC_OMP isn't really needed, any more, except for .. what? clang and Apple? I only use OC_OMP in one place ... but .. well, I noticed something was wrong ...

[linas]

Actually, this doesn't fix it either, somethings still wrong. OC_OMP is still not defined, even though cmake prints: C++ library standardizes parallelism ... so this is more of a bug-report than a pull-req ....

Oh .. I see, there is also this:

IF (PARALLEL_STL_FOUND)
   ADD_DEFINITIONS(-DHAVE_PARALLEL_STL)
ENDIF (PARALLEL_STL_FOUND)

but that is not working ... arghh...