Issue #15984: Merge PyUnicode doc from 3.5

Modules/_heapqmodule.c

@@ -550,7 +550,7 @@ representation for a tournament.  The numbers below are `k', not a[k]:\n\
 \n\
 \n\
 In the tree above, each cell `k' is topping `2*k+1' and `2*k+2'.  In\n\
-an usual binary tournament we see in sports, each cell is the winner\n\
+a usual binary tournament we see in sports, each cell is the winner\n\
 over the two cells it tops, and we can trace the winner down the tree\n\
 to see all opponents s/he had.  However, in many computer applications\n\
 of such tournaments, we do not need to trace the history of a winner.\n\

Modules/_pickle.c

@@ -1119,7 +1119,7 @@ _Unpickler_SkipConsumed(UnpicklerObject *self)
         return 0;
 
     assert(self->peek);  /* otherwise we did something wrong */
-    /* This makes an useless copy... */
+    /* This makes a useless copy... */
     r = PyObject_CallFunction(self->read, "n", consumed);
     if (r == NULL)
         return -1;

Modules/_tracemalloc.c

@@ -379,7 +379,7 @@ tracemalloc_get_frame(PyFrameObject *pyframe, frame_t *frame)
 
     if (!PyUnicode_Check(filename)) {
 #ifdef TRACE_DEBUG
-        tracemalloc_error("filename is not an unicode string");
+        tracemalloc_error("filename is not a unicode string");
 #endif
         return;
     }