coding style: fix yield used as a function

tests/test-check-code.t

@@ -1,95 +1,95
   $ cat > correct.py <<EOF
   > def toto(arg1, arg2):
   >     del arg2
   >     return (5 + 6, 9)
   > EOF
   $ cat > wrong.py <<EOF
   > def toto( arg1, arg2):
   >     del(arg2)
   >     return ( 5+6, 9)
   > EOF
   $ cat > quote.py <<EOF
   > # let's use quote in comments
   > (''' ( 4x5 )
   > but """\\''' and finally''',
   > """let's fool checkpatch""", '1+2',
   > '"""', 42+1, """and
   > ( 4-1 ) """, "( 1+1 )\" and ")
   > a, '\\\\\\\\', "\\\\\\" x-2", "c-1"
   > EOF
   $ cat > non-py24.py <<EOF
   > # Using builtins that does not exist in Python 2.4
   > if any():
   >     x = all()
   >     y = format(x)
   > 
   > # Do not complain about our own definition
   > def any(x):
   >     pass
   > EOF
   $ check_code="$TESTDIR"/../contrib/check-code.py
   $ "$check_code" ./wrong.py ./correct.py ./quote.py ./non-py24.py
   ./wrong.py:1:
    > def toto( arg1, arg2):
    gratuitous whitespace in () or []
   ./wrong.py:2:
    >     del(arg2)
-   del isn't a function
+   Python keyword is not a function
   ./wrong.py:3:
    >     return ( 5+6, 9)
    missing whitespace in expression
    gratuitous whitespace in () or []
   ./quote.py:5:
    > '"""', 42+1, """and
    missing whitespace in expression
   ./non-py24.py:2:
    > if any():
    any/all/format not available in Python 2.4
   ./non-py24.py:3:
    >     x = all()
    any/all/format not available in Python 2.4
   ./non-py24.py:4:
    >     y = format(x)
    any/all/format not available in Python 2.4
   [1]
 
   $ cat > is-op.py <<EOF
   > # is-operator comparing number or string literal
   > x = None
   > y = x is 'foo'
   > y = x is "foo"
   > y = x is 5346
   > y = x is -6
   > y = x is not 'foo'
   > y = x is not "foo"
   > y = x is not 5346
   > y = x is not -6
   > EOF
 
   $ "$check_code" ./is-op.py
   ./is-op.py:3:
    > y = x is 'foo'
    object comparison with literal
   ./is-op.py:4:
    > y = x is "foo"
    object comparison with literal
   ./is-op.py:5:
    > y = x is 5346
    object comparison with literal
   ./is-op.py:6:
    > y = x is -6
    object comparison with literal
   ./is-op.py:7:
    > y = x is not 'foo'
    object comparison with literal
   ./is-op.py:8:
    > y = x is not "foo"
    object comparison with literal
   ./is-op.py:9:
    > y = x is not 5346
    object comparison with literal
   ./is-op.py:10:
    > y = x is not -6
    object comparison with literal
   [1]