BUG: dtype=object should stop conversion from object in frame constructo...

[changhiskhan]

...r #2255

don't call maybe_convert_objects in _convert_object_array if dtype is object.

Note that it also stops other type conversions too.

[ghost]

It's better to add new keyword arguments at the end of the arglist,
or you risk breaking existing code:

In [2]: def f(a,b=1):
   ...:    print b
   ...: 
   ...: f(0,'b')
   ...: 
b

In [3]: def f(a,c=2,b=1):
   ...:    print b
   ...: 
   ...: f(0,'b')
1