Stackless issue python#217: C-API documentation update

Update the names of watchdog flags to match the implementation.

(cherry picked from commit 05dfdf5)

Author: Anselm Kruis

Doc/c-api/stackless.rst

@@ -327,17 +327,17 @@ stackless module
      it will be awakened by other threads using channels which its
      blocked tasklets are waiting on.
 
-  ``Py_WATCHDOG_SOFT``
+  ``PY_WATCHDOG_SOFT``
      Instead of interrupting a tasklet, we wait until the
      next tasklet scheduling moment to return.  Always returns
      *Py_None*, as everything is in order.
 
-  ``Py_WATCHDOG_IGNORE_NESTING``
+  ``PY_WATCHDOG_IGNORE_NESTING``
      Allows interrupts at all levels, effectively acting as
      though the *ignore_nesting* attribute were set on all
      tasklets.
 
-  ``Py_WATCHDOG_TIMEOUT``
+  ``PY_WATCHDOG_TIMEOUT``
      Interprets *timeout* as a fixed run time, rather than a
      per-tasklet run limit.  The function will then attempt to
      interrupt execution once this many total opcodes have

Stackless/changelog.txt

@@ -10,6 +10,10 @@ What's New in Stackless 2.7.XX?
 
 *Release date: XXXX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/217
+  C-API documentation update: update the names of watchdog flags to match the
+  implementation.
+
 - https://github.com/stackless-dev/stackless/issues/222
   Fix a bug that could cause an assertion failure and a reference leak during
   the termination of a main-tasklet, if an application embeds Stackless Python.

Stackless/stackless_api.h

@@ -334,18 +334,21 @@ PyAPI_FUNC(long) PyStackless_GetCurrentId(void);
  *   When set enables the old thread-blocking behaviour when
  *   we run out of tasklets on this thread and there are other
  *   Python(r) threads running.
- * Py_WATCHDOG_SOFT:
+ * PY_WATCHDOG_SOFT:
  *   Instead of interrupting a tasklet, we wait until the
  *   next tasklet scheduling moment to return.  Always returns
  *   Py_None, as everything is in order.
- * Py_WATCHDOG_IGNORE_NESTING:
+ * PY_WATCHDOG_IGNORE_NESTING:
  *   allows interrupts at all levels, effectively acting as
  *   though the "ignore_nesting" attribute were set on all
  *   tasklets.
- * Py_WATCHDOG_TIMEOUT:
+ * PY_WATCHDOG_TIMEOUT:
  *   interprets 'timeout' as a total timeout, rather than a
  *   timeslice length.  The function will then attempt to
- *   interrupt execution 
+ *   interrupt execution
+ *
+ * Note: the spelling is inconsistent (Py_ versus PY_) since ever.
+ *       We won't change it for compatibility reasons.
  */
 #define Py_WATCHDOG_THREADBLOCK		1
 #define PY_WATCHDOG_SOFT			2