Making Gnumeric -Werror friendly (well, almost).

* plugins/excel/ms-chart.c: Added "#if 0/#endif" around declarations
of unused variables.

* plugins/gda/plugin-gda.c (display_recordset): Removed unused
variable, fixed some errors (that's why I use -Werror).

* plugins/xml2/xml2.c (init_plugin): Used xml2_probe function.

* src/search.c: Included "ranges.h".

* src/style.c: Included "sheet.h"