Add support for named buffers. If you don't name a buffer, things work

much as before - buffers are automatically named "buffer0000",
"buffer0001" and so on and ordered as a stack. Buffers can be named
explicitly when creating ("loadb -b foo" etc) or renamed ("setb -b
buffer0000 -n foo"). If buffers are named explicitly, they are not
deleted when buffer-limit is reached. Diff from J Raynor.

format.c

@@ -608,6 +608,7 @@ format_paste_buffer(struct format_tree *ft, struct paste_buffer *pb,
 	char	*s;
 
 	format_add(ft, "buffer_size", "%zu", pb->size);
+	format_add(ft, "buffer_name", "%s", pb->name);
 
 	s = paste_make_sample(pb, utf8flag);
 	format_add(ft, "buffer_sample", "%s", s);