#137 Fix no source and lineno was set to caption of table

[Takeshi KOMIYA]

In Sphinx, we use source and line information of text nodes for I18N feature.

In docutils-0.13.2, it seems a caption of table does not have both attributes. The table node (parent) don't have also.
The attached patch sets the source and line information to the caption node.

Could you review this please?

Note: it seems there are no test cases for source and lines. So I simply added the directive code. Please let me know if any good place to do that.

Thanks,

[Brecht Machiels]

Related: https://sourceforge.net/p/docutils/feature-requests/41/

[Günter Milde]

Applied in Revision 8039.