Fix #271

[cstjean]

When I translated the IO code to @pydef, I neglected to bring in that check from the jl_io_flush function.

[stevengj]

Add a test case using PyObject(IOBuffer())[:flush]()?

[coveralls]

Coverage increased (+0.1%) to 59.511% when pulling 31a80a2 on cstjean:pull-request/31a80a21 into 71495c1 on stevengj:master.

[cstjean]

Like this?

[stevengj]

Great, thanks.

[stevengj]

I've added you as a collaborator; feel free to merge when the tests are green.

[stevengj]

And feel free to tag as a new patch release (1.6.1, I think).

[coveralls]

Coverage increased (+0.1%) to 59.511% when pulling a551fa2 on cstjean:pull-request/31a80a21 into 71495c1 on stevengj:master.