TST: remove ResourceWarnings

[jreback]

So just enabled ResourceWarnings to show up (these are only on PY3), see a sample run here; they are only enabled on the 3.5-dev build (you can manually enable by setting PANDAS_TESTING_MODE="deprecate"

These are unclosed filehandles mostly in the read_csv tests.

So there are 2 cases here which need to be dealt with:

• when we uncompress things, we create a wrapper around the decompressor, these need to be closed, ONLY if the original handle was a string (IOW a pth), and NOT a filehandle itself (which we need to leave open)
• when we have a utf-16 encoding we create a UTFReader object which needs to be closed (but same as above, you can't close it if the original handle was open to begin with)

So I added some .close() methods to the readers, but they are not explicity called anywhere. We need to figure out when to do this.

This might be a bit non-trivial!

[gfyoung]

@jreback: IINM, this issue was fixed in #13940.

[jreback]

right