Create Layer for accessing ArcGIS Server.

[jeffadams78]

I'm attaching the appropriate layer class, examples, and unit tests.

It uses ArcGIS Server 9.3's REST API. The main advantage over WMS is that this allows filtering of features returned, which ArcGIS Server's WMS interface does not support.

[jeffadams78]

Patch file for ArcGIS Server Layer support.

[jeffadams78]

New example file using ArcGIS Server

[jeffadams78]

New Layer for accessing ArcGIS Server natively.

[jeffadams78]

New unit test file for ArcGIS Server layer.

[jeffadams78]

All attachments are uploaded, ready for review.

[jeffadams78]

FYI: I believe my boss has already filled out a "Corporate Contributor License Agreement". -- Jeff Adams, Avencia Inc.

[crschmidt]

(In [8917]) Create a Layer class to access the ArcGIS 9.3 Map Export service. Patch by Jeff Adams, from Avencia. r=me. Tested with the default service, and several other example map services from ESRI (like  http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/export).

Note that I don't believe this takes advantage of map caches; if we create a seperate layer for that, we should probably create a Layer.ArcGIS. namespace.

(Closes #1749)