fix testcases assuming char is signed (thanks to Yaroslav Halchenko)

tests/run/c_int_types_T255.pyx

@@ -93,10 +93,10 @@ def test_char(char x):
    Traceback (most recent call last):
        ...
    OverflowError: ...
+   >>> if CHAR_MIN < 0: 
+   ...     assert test_char(-1) == -1
    >>> test_char(CHAR_MIN) == CHAR_MIN
    True
-   >>> test_char(-1)
-   -1
    >>> test_char(0)
    0
    >>> test_char(1)

tests/run/dictintindex.pyx

@@ -4,7 +4,10 @@ def test_get_char_neg():
     0
     """
     cdef char key = -1
+    if <char>-1 < 0:
         d = {-1:0}
+    else:
+        d = {255:0}
     return d[key]
 def test_get_char_zero():
     """