check-code: disallow use of hasattr()

The hasattr() builtin from Python < 3.2 [1] has slightly surprising
behavior: it catches all exceptions, even KeyboardInterrupt. This
causes it to have several surprising side effects, such as hiding
warnings that occur during attribute load and causing mysterious
failure modes when ^Cing an application. In later versions of Python
2.x [0], exception classes which do not inherit from Exception (such
as SystemExit and KeyboardInterrupt) are not caught, but other types
of exceptions may still silently cause returning False instead of
getting a reasonable exception.

[0] http://bugs.python.org/issue2196
[1] http://docs.python.org/dev/whatsnew/3.2.html

contrib/check-code.py

@@ -148,7 +148,7 b' pypats = ['
     (r'(?<!def)\s+(any|all|format)\(',
      "any/all/format not available in Python 2.4"),
     (r'(?<!def)\s+(callable)\(',
-     "callable not available in Python 3, use hasattr(f, '__call__')"),
+     "callable not available in Python 3, use getattr(f, '__call__', None)"),
     (r'if\s.*\selse', "if ... else form not available in Python 2.4"),
     (r'^\s*(%s)\s\s' % '|'.join(keyword.kwlist),
      "gratuitous whitespace after Python keyword"),
@@ -168,6 +168,8 b' pypats = ['
      "comparison with singleton, use 'is' or 'is not' instead"),
     (r'^\s*(while|if) [01]:',
      "use True/False for constant Boolean expression"),
+    (r'(?<!def)\s+hasattr',
+     'hasattr(foo, bar) is broken, use util.safehasattr(foo, bar) instead'),
     (r'opener\([^)]*\).read\(',
      "use opener.read() instead"),
     (r'opener\([^)]*\).write\(',