Issue #5341: Fix a variety of spelling errors.

Objects/abstract.c

@@ -2258,7 +2258,7 @@ PySequence_Fast(PyObject *v, const char *m)
 
 /* Iterate over seq.  Result depends on the operation:
    PY_ITERSEARCH_COUNT:  -1 if error, else # of times obj appears in seq.
-   PY_ITERSEARCH_INDEX:  0-based index of first occurence of obj in seq;
+   PY_ITERSEARCH_INDEX:  0-based index of first occurrence of obj in seq;
    	set ValueError and return -1 if none found; also return -1 on error.
    Py_ITERSEARCH_CONTAINS:  return 1 if obj in seq, else 0; -1 on error.
 */

Objects/listsort.txt

@@ -309,7 +309,7 @@ Stability constrains permissible merging patterns.  For example, if we have
     A:10000  B:20000  C:10000
 
 we dare not merge A with C first, because if A, B and C happen to contain
-a common element, it would get out of order wrt its occurence(s) in B.  The
+a common element, it would get out of order wrt its occurrence(s) in B.  The
 merging must be done as (A+B)+C or A+(B+C) instead.
 
 So merging is always done on two consecutive runs at a time, and in-place,

Objects/object.c

@@ -1964,7 +1964,7 @@ static void
 none_dealloc(PyObject* ignore)
 {
 	/* This should never get called, but we also don't want to SEGV if
-	 * we accidently decref None out of existance.
+	 * we accidentally decref None out of existence.
 	 */
 	Py_FatalError("deallocating None");
 }

Objects/unicodeobject.c

@@ -1704,7 +1704,7 @@ PyObject *PyUnicode_EncodeUTF7(const Py_UNICODE *s,
                 charsleft = (charsleft << 16) | ch;
                 /* out, charsleft, bitsleft = */ ENCODE(out, charsleft, bitsleft);
 
-                /* If the next character is special then we dont' need to terminate
+                /* If the next character is special then we don't need to terminate
                    the shift sequence. If the next character is not a BASE64 character
                    or '-' then the shift sequence will be terminated implicitly and we
                    don't have to insert a '-'. */