Issue #4806: Avoid masking TypeError when *-unpacking a generator

Based on patch by Hagen Fürstenau.
diff --git a/Lib/test/test_extcall.py b/Lib/test/test_extcall.py
index 80e09a0..babcce9 100644
--- a/Lib/test/test_extcall.py
+++ b/Lib/test/test_extcall.py
@@ -93,7 +93,7 @@
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be a sequence, not instance
+    TypeError: g() argument after * must be an iterable, not instance
 
     >>> class Nothing:
     ...     def __len__(self): return 5
@@ -102,7 +102,7 @@
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be a sequence, not instance
+    TypeError: g() argument after * must be an iterable, not instance
 
     >>> class Nothing():
     ...     def __len__(self): return 5
@@ -128,6 +128,17 @@
     >>> g(*Nothing())
     0 (1, 2, 3) {}
 
+Check for issue #4806: Does a TypeError in a generator get propagated with the
+right error message?
+
+    >>> def broken(): raise TypeError("myerror")
+    ...
+
+    >>> g(*(broken() for i in range(1)))
+    Traceback (most recent call last):
+      ...
+    TypeError: myerror
+
 Make sure that the function doesn't stomp the dictionary
 
     >>> d = {'a': 1, 'b': 2, 'c': 3}
@@ -167,17 +178,17 @@
     >>> h(*h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after * must be a sequence, not function
+    TypeError: h() argument after * must be an iterable, not function
 
     >>> dir(*h)
     Traceback (most recent call last):
       ...
-    TypeError: dir() argument after * must be a sequence, not function
+    TypeError: dir() argument after * must be an iterable, not function
 
     >>> None(*h)
     Traceback (most recent call last):
       ...
-    TypeError: NoneType object argument after * must be a sequence, \
+    TypeError: NoneType object argument after * must be an iterable, \
 not function
 
     >>> h(**h)