Fix typos in comments, docs and test names (#15018)

* Fix typos in comments, docs and test names

* Update test_pyparse.py

account for change in string length

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: Dealloccte -> Deallocate

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Update posixmodule checksum.

* Reverse idlelib changes.
diff --git a/Include/abstract.h b/Include/abstract.h
index f36fafb..8951f63 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -702,7 +702,7 @@
      (PyList_Check(o) ? PyList_GET_ITEM(o, i) : PyTuple_GET_ITEM(o, i))
 
 /* Return a pointer to the underlying item array for
-   an object retured by PySequence_Fast */
+   an object returned by PySequence_Fast */
 #define PySequence_Fast_ITEMS(sf) \
     (PyList_Check(sf) ? ((PyListObject *)(sf))->ob_item \
                       : ((PyTupleObject *)(sf))->ob_item)
diff --git a/Include/ast.h b/Include/ast.h
index f1d7348..1347fcf 100644
--- a/Include/ast.h
+++ b/Include/ast.h
@@ -25,7 +25,7 @@
 PyAPI_FUNC(PyObject *) _PyAST_ExprAsUnicode(expr_ty);
 
 /* Return the borrowed reference to the first literal string in the
-   sequence of statemnts or NULL if it doesn't start from a literal string.
+   sequence of statements or NULL if it doesn't start from a literal string.
    Doesn't set exception. */
 PyAPI_FUNC(PyObject *) _PyAST_GetDocString(asdl_seq *);
 
diff --git a/Include/pymath.h b/Include/pymath.h
index 6cf69f9..f869724 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -125,7 +125,7 @@
 
 /* Py_IS_FINITE(X)
  * Return 1 if float or double arg is neither infinite nor NAN, else 0.
- * Some compilers (e.g. VisualStudio) have intrisics for this, so a special
+ * Some compilers (e.g. VisualStudio) have intrinsics for this, so a special
  * macro for this particular test is useful
  * Note: PC/pyconfig.h defines Py_IS_FINITE as _finite
  */