Fix ArcGIS WFS Features Parsing Error

Hi Maintainer,

While using Geotools in our project, I found a when parsing WFS GetFeature response from ArcGIS Server 10.1: unable to handle the missing attribute "gml:id"

Unlike a standard WFS GetFeature response, the attribute "gml:id" is missing for EACH FEATURE in ArcGIS response. (see http://resources.arcgis.com/en/help/main/10.1/index.html#//0154000004rz000000, search for "gml:ids") However, this is a mandatory attribute in org.geotools.data.wfs.v1_1_0.parwers.XMLSimpleFeatureParser.java 

I have included a Test Case ArcGISFeaturesParserTest.java. So that you could test it. When you run this test case in unfixed version, you will find the FeatureCollection returns empty which means it does not parsed the Features. 

I have also filed a JIRA issue. http://jira.codehaus.org/browse/GEOT-4710 

This is the first time I try to contribute to geotools community. So hopefully I did not do a lot of "wrongs". Please let me know if you want anything more/else. 

Thanks,
Allen