[WMS] Need a way to control fields to return in text/plain GetFeatureInfo output

[dmorissette]

Currently there is no way to control which attributes are output in the
text/plain GetFeatureInfo output. By default all fields are always returned.

We need to add a mechanism to specify which fields to output, I propose to use a
mechanism similar to what we have for GML (see bug 950 comment 16):

  wms_featureinfo_textplain_include_items: comma delimited list or keyword 'all'
  wms_featureinfo_textplain_exclude_items: comma delimited list (all items are
excluded by default)

This would imply the same behavior change for text/plain that was introduced for
GML by bug 950, i.e. that by default text/plain output would return no
attributes unless you explicitly set wms_textplain_include_items.

[dmorissette]

Working on this now.

[dmorissette]

Done in v4.9 CVS.

Note that in the end I went with the same metadata names that are used in mapgml.c:

  wms/ows_include_items: comma delimited list or keyword 'all'
  wms/ows_exclude_items: comma delimited list (all items are excluded by default)

I also modified mapgml.c to accept wms_include_items and wms_exclude_items. It
used to look only for ows_*, wfs_* and gml_*.

I still need to update docs

[dmorissette]

I have added a comment about this at the bottom of the WMS-Server-HOWTO in the
website:
http://mapserver.gis.umn.edu/docs/howto/wms_server

I'll let Jeff integrate this the way he likes in his document.