Clean up task private data.

[Reviewed by sungeun.]

As a result of several recent commits, we are no longer using anything
in the task private data (chpl_task_private_data_t) except the serial
state of the task.  In addition, there isn't an obvious need to have the
task private data be part of the public tasking interface.  This commit
cleans up the task private data and moves the definition from the public
interface into the implementations.

The specific file changes are as follows.

compiler/include/primitive.h
compiler/AST/primitive.cpp
compiler/AST/expr.cpp
compiler/AST/checkAST.cpp
compiler/optimizations/optimizeOnClauses.cpp
  Remove PRIM_IS_HERE, which is no longer used.

runtime/include/chpl-gen-includes.h
  Remove chpl_is_here(), which was only used by PRIM_IS_HERE.

runtime/include/chpl-tasks.h
  Remove the task private data struct declaration, as well as the
  chpl_{alloc,calloc,realloc,free}_fn() function type declarations that
  support it.
  Remove decarations for interface functions that are no longer needed:
    chpl_task_getPrivateData()
    chpl_task_{get,set}Here()
    chpl_task_{get,set}LocaleID()
  Remove a comment that is no longer applicable.

runtime/src/tasks/fifo/tasks-fifo.c
runtime/src/tasks/none/tasks-none.c
runtime/src/tasks/massivethreads/tasks-massivethreads.c
third-party/qthread/qthread-1.10/src/interfaces/chapel/tasks-qthreads.c
  Add a declaration for task private data declaration, private to the
  tasking implementation.  Use that in place of the old public one
  Remove interface functions that are no longer needed:
    chpl_task_getPrivateData()
    chpl_task_{get,set}Here()
    chpl_task_{get,set}LocaleID()
  In qthreads tasking, also remove #include "chpl-mem.h", which we don't
  need any more.

third-party/qthread/qthread-1.10/src/Makefile.in
third-party/qthread/qthread-1.10/src/interfaces/chapel/Makefile.inc
  Remove -I$CHPL_HOME/runtime/include/mem/$CHPL_MAKE_MEM.  Without the
  #include "chpl-mem.h", we don't need to be able to get to the memory
  implementation-specific include files any more.


git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@21856 3a8e244f-b0f2-452b-bcba-4c88e055c3ca