cgi param substitute for metadata

[Charlton Purvis]

Hi, folks:

I'm not sure if this interests anyone or not, but I've continued to make
changes to mapserv.c to look for %cgi_vars% for runtime substitutions.

It has been particularly useful for only returning columns from a shapefile
that match whatever time parameter a user has passed.

E.g.

METADATA
  "gml_include_items" "StartTime,t%STEP_TIME%,v%STEP_TIME%"
END

Because I may have columns called something like t05110817 and v05110817.
And I don't want to return all the timestamps -- just these.

It's been WAY too long since I tried dereferencing hashes in C, but this
blurp of code does the trick.  It's probably inefficient since I'm
destroying an item and then recreating it.

Inside mapObj *loadMap(void)
...
      tmp_metadata_item = msLookupHashTable(&(map->layers[j].metadata),
"gml_include_items");
      if(tmp_metadata_item && (strstr(tmp_metadata_item, tmpstr) != NULL)) {
        tmp_metadata_item = gsub(tmp_metadata_item, tmpstr,
msObj->request->ParamValues[i]);
        if(msRemoveHashTable(&(map->layers[j].metadata),
"gml_include_items")) {
          msInsertHashTable(&(map->layers[j].metadata), "gml_include_items",
tmp_metadata_item);
        }
      }
...

Charlton