Bug #1550983: emit better error messages for erroneous relative
imports (if not in package and if beyond toplevel package).
 (backport from rev. 51765)
diff --git a/Python/import.c b/Python/import.c
index a0c5055..5af3651 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -2114,7 +2114,7 @@
 		size_t len;
 		if (lastdot == NULL && level > 0) {
 			PyErr_SetString(PyExc_ValueError,
-					"Relative importpath too deep");
+				"Attempted relative import in non-package");
 			return NULL;
 		}
 		if (lastdot == NULL)
@@ -2133,7 +2133,8 @@
 		char *dot = strrchr(buf, '.');
 		if (dot == NULL) {
 			PyErr_SetString(PyExc_ValueError,
-					"Relative importpath too deep");
+				"Attempted relative import beyond "
+				"toplevel package");
 			return NULL;
 		}
 		*dot = '\0';