Merge branch 'ds/sparse-add'

"git sparse-checkout" learned a new "add" subcommand.

* ds/sparse-add:
  sparse-checkout: allow one-character directories in cone mode
  sparse-checkout: work with Windows paths
  sparse-checkout: create 'add' subcommand
  sparse-checkout: extract pattern update from 'set' subcommand
  sparse-checkout: extract add_patterns_from_input()

dir.c

@@ -688,7 +688,7 @@ static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern
 		return;
 	}
 
-	if (given->patternlen <= 2 ||
+	if (given->patternlen < 2 ||
 	    *given->pattern == '*' ||
 	    strstr(given->pattern, "**")) {
 		/* Not a cone pattern. */