Fix off-by-one errors in code to find depth of stack.

XXX The code is still widely inaccurate, but most (all?) of the time
it's an overestimate.
diff --git a/Lib/compiler/pyassem.py b/Lib/compiler/pyassem.py
index b2f91aa..413a954 100644
--- a/Lib/compiler/pyassem.py
+++ b/Lib/compiler/pyassem.py
@@ -764,11 +764,11 @@
     # UNPACK_SEQUENCE, BUILD_TUPLE,
     # BUILD_LIST, CALL_FUNCTION, MAKE_FUNCTION, BUILD_SLICE
     def UNPACK_SEQUENCE(self, count):
-        return count
+        return count-1
     def BUILD_TUPLE(self, count):
-        return -count
+        return -count+1
     def BUILD_LIST(self, count):
-        return -count
+        return -count+1
     def CALL_FUNCTION(self, argc):
         hi, lo = divmod(argc, 256)
         return lo + hi * 2