XML format enhancements for GML and Atom formats

add readers/writers and shorthand methods for applying them

A few comments:

lib/OpenLayers/Format/XML.js:

• Very minor:

   	440	            for(prefix in this.namespaces) { 
   	441	                if(this.namespaces[prefix] == uri) { 
   	442	                    gotPrefix = true; 
   	443	                    break; 
   	444	                } 
   	445	            } 
   	446	            if(!gotPrefix) { 
   	447	                prefix = null; 
   	448	            } 
  

  would maybe look better like this:

   	440	            for(var p in this.namespaces) { 
   	441	                if(this.namespaces[prefix] == uri) { 
   	442	                    prefix = p; 
   	443	                    break; 
   	444	                } 
   	445	            } 
  

• unclear ND comment L534, could be changed to something like:

   	529	     * Parameters: 
   	530	     * node - {DOMElement} The node to be read (required). 
   	531	     * obj - {Object} The object to be modified (optional). 
   	532	     * 
   	533	     * Returns: 
   	534	     * {Object} The input object, modified (or a new one if none was passed). 
  

lib/OpenLayers/Format.js:

• I do not see what Format.options is needed for, but since there is a test for it, I'm sure there is a reason. So if there really is:
• Format.options is an undocumented property -- should be added as Property and ND-commented.

After those modification and clarification of Format.options, this is good to commit. Thanks for this patch tim, this makes format writers' lives a lot easier.

(In [7982]) Adding readers and writers properties to xml formats. These will contain public functions used in serializing and deserializing various formats. Shorthand methods for calling these readers & writers are writeNode and readNode. r=ahocever (closes #1722)

just a reminder: if you want your patch to go from trunk to branch, gotta mark it 'pullup'.

(In [8012]) Batch merge for rc2 of 2.7. 'svn merge -r7967:HEAD from trunk (Closes #1733) (Closes #1489) (Closes #1639) (Closes #1718) (Closes #1723) (Closes #1732) (Closes #1616) (Closes #1722)