index: use PyMem_Free() to free nodeetree instance

As Yuya pointed out in the review of D4108, PyMem_Malloc() and
PyMem_Free() should be paired. IIUC, PyMem_Malloc() may use a
different allocator than malloc(), so using free() with a pointer from
PyMem_Malloc() may be very wrong.

Differential Revision: https://phab.mercurial-scm.org/D4152

mercurial/cext/revlog.c

@@ -323,7 +323,7 b' static void _index_clearcaches(indexObje'
 	}
 	if (self->nt != NULL) {
 		free(self->nt->nodes);
-		free(self->nt);
+		PyMem_Free(self->nt);
 	}
 	self->nt = NULL;
 	Py_CLEAR(self->headrevs);
@@ -1106,7 +1106,7 b' static int nt_init(indexObject *self)'
 
 		self->nt->nodes = calloc(self->nt->capacity, sizeof(nodetreenode));
 		if (self->nt->nodes == NULL) {
-			free(self->nt);
+			PyMem_Free(self->nt);
 			self->nt = NULL;
 			PyErr_NoMemory();
 			return -1;
@@ -1119,7 +1119,7 b' static int nt_init(indexObject *self)'
 		self->nt->length = 1;
 		if (nt_insert(self, nullid, -1) == -1) {
 			free(self->nt->nodes);
-			free(self->nt);
+			PyMem_Free(self->nt);
 			self->nt = NULL;
 			return -1;
 		}