cpukit: deprecate task variables. closes #2293.

doc/user/task.t

@@ -308,6 +308,8 @@ generally result in an exception condition.
 
 @cindex per task variables
 
+Per task variables are deprecated, see the warning below.
+
 Per task variables are used to support global variables whose value
 may be unique to a task. After indicating that a variable should be
 treated as private (i.e. per-task) the task can access and modify the
@@ -346,6 +348,9 @@ that task is the logical owner of the value in the per-task variable's
 location. There is no way for a single memory image to contain the
 correct value for each task executing on each core. Consequently,
 per-task variables are disabled in SMP configurations of RTEMS.
+Instead the application developer should
+consider the use of POSIX Keys or Thread Local Storage (TLS). POSIX Keys
+are not enabled in all RTEMS configurations.
 
 @subsection Building a Task Attribute Set
 
@@ -1787,6 +1792,8 @@ passed to the destructor function is the task's value of the variable.
 
 @subheading NOTES:
 
+This directive is deprecated and task variables will be removed.
+
 Task variables increase the context switch time to and from the
 tasks that own them so it is desirable to minimize the number of
 task variables.  One efficient method
@@ -1844,6 +1851,8 @@ task, which can get its private value by directly accessing the variable.
 
 @subheading NOTES:
 
+This directive is deprecated and task variables will be removed.
+
 If you change memory which @code{task_variable_value} points to,
 remember to declare that memory as volatile, so that the compiler
 will optimize it correctly.  In this case both the pointer
@@ -1895,6 +1904,8 @@ This directive removes the given location from a task's context.
 
 @subheading NOTES:
 
+This directive is deprecated and task variables will be removed.
+
 Per-task variables are disabled in SMP configurations and this service
 is not available.