SPR-8863 Add RequestContext.getPathToServlet() method.

This method allows a view to access the combined context path and
servlet mapping path for prefixing URLs without having to specify
the literal part of a servlet mapping such as "/main/*") 
explicitly everywhere. For example:

${requestContext.pathToServlet}/css/main.css

org.springframework.web/src/main/java/org/springframework/web/util/UrlPathHelper.java

@@ -280,6 +280,20 @@ public class UrlPathHelper {
 		return decodeRequestString(request, contextPath);
 	}
 
+	/**
+	 * Return the servlet path for the given request, detecting an include request
+	 * URL if called within a RequestDispatcher include.
+	 * @param request current HTTP request
+	 * @return the servlet path
+	 */
+	public String getOriginatingServletPath(HttpServletRequest request) {
+		String servletPath = (String) request.getAttribute(WebUtils.FORWARD_SERVLET_PATH_ATTRIBUTE);
+		if (servletPath == null) {
+			servletPath = request.getServletPath();
+		}
+		return servletPath;
+	}
+
 	/**
 	 * Return the query string part of the given request's URL. If this is a forwarded request,
 	 * correctly resolves to the query string of the original request.