fetch --prune: Run prune before fetching

When we have a remote-tracking branch named "frotz/nitfol" from a
previous fetch, and the upstream now has a branch named "frotz",
fetch would fail to remove "frotz/nitfol" with a "git fetch --prune"
from the upstream. git would inform the user to use "git remote
prune" to fix the problem.

Change the way "fetch --prune" works by moving the pruning operation
before the fetching operation. This way, instead of warning the user
of a conflict, it autmatically fixes it.

Signed-off-by: Tom Miller <jackerran@gmail.com>
Tested-by: Thomas Rast <tr@thomasrast.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 1b81cf9..09825c8 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -863,11 +863,6 @@
 
 	if (tags == TAGS_DEFAULT && autotags)
 		transport_set_option(transport, TRANS_OPT_FOLLOWTAGS, "1");
-	if (fetch_refs(transport, ref_map)) {
-		free_refs(ref_map);
-		retcode = 1;
-		goto cleanup;
-	}
 	if (prune) {
 		/*
 		 * We only prune based on refspecs specified
@@ -883,6 +878,11 @@
 				   transport->url);
 		}
 	}
+	if (fetch_refs(transport, ref_map)) {
+		free_refs(ref_map);
+		retcode = 1;
+		goto cleanup;
+	}
 	free_refs(ref_map);
 
 	/* if neither --no-tags nor --tags was specified, do automated tag