Include method and URL in curl error (#214)

In case curl gives an error, it's helpful to know the URL
being tried and the method. In the GET case, one can easily
retry in the shell and debug this.

letsencrypt.sh

@@ -332,7 +332,7 @@ http_request() {
   set -e
 
   if [[ ! "${curlret}" = "0" ]]; then
-    _exiterr "Problem connecting to server (curl returned with ${curlret})"
+    _exiterr "Problem connecting to server (${1} for ${2}; curl returned with ${curlret})"
   fi
 
   if [[ ! "${statuscode:0:1}" = "2" ]]; then