Add latex fragment exporter of visible rows only. [#739512]

2014-11-02  Andreas J. Guelzow <aguelzow@pyrshep.ca>

	* latex.c (latex_table_file_save_impl): new
	(latex_table_file_save): use latex_table_file_save_impl
	(latex_table_visible_file_save): new
	* plugin.xml.in: add latex_table_visible_file_save
	* latex.h (latex_table_visible_file_save): new