Merge branch 'jc/cache-unmerge'

* jc/cache-unmerge:
  rerere forget path: forget recorded resolution
  rerere: refactor rerere logic to make it independent from I/O
  rerere: remove silly 1024-byte line limit
  resolve-undo: teach "update-index --unresolve" to use resolve-undo info
  resolve-undo: "checkout -m path" uses resolve-undo information
  resolve-undo: allow plumbing to clear the information
  resolve-undo: basic tests
  resolve-undo: record resolved conflicts in a new index extension section
  builtin-merge.c: use standard active_cache macros

Conflicts:
	builtin-ls-files.c
	builtin-merge.c
	builtin-rerere.c

builtin-read-tree.c

@@ -13,6 +13,7 @@
 #include "dir.h"
 #include "builtin.h"
 #include "parse-options.h"
+#include "resolve-undo.h"
 
 static int nr_trees;
 static struct tree *trees[MAX_UNPACK_TREES];
@@ -124,6 +125,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			die("You need to resolve your current index first");
 		stage = opts.merge = 1;
 	}
+	resolve_undo_clear();
 
 	for (i = 0; i < argc; i++) {
 		const char *arg = argv[i];