Consolidate the include statements scattered across the code in accordance
with the comment in C4Include.h. The advantages are listed in the same
comment.
Furthermore, it follows llvm-include-order which is the logical
extrapolation of the project's style guideline wherever possible
(C4Include.h being the most-frequent exception).
procedure is meant to be run on, so introduce yet another StdScheduler
extra method StartOnCurrentThread which on Mac OS X does the actual run
loop registration stuff and needs to be called from the actual thread
the scheduler is supposed to run on
StdSchedulerMac: Remove SCHAdditions objects again