scan_path(): Do not recurse into hidden directories by default

Paths that start with a period ('.') are considered hidden in the Unix world.
scan_path() should arguably not recurse into these directories by default.
This patch makes it so, and introduces the "scan-hidden-path" config variable
for overriding the new default and revert to the old behaviour (scanning _all_
directories, including hidden .directories).

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Lars Hjemli <larsh@prediktor.no>
diff --git a/scan-tree.c b/scan-tree.c
index eda8c67..627af1b 100644
--- a/scan-tree.c
+++ b/scan-tree.c
@@ -183,6 +183,8 @@
 				continue;
 			if (ent->d_name[1] == '.' && ent->d_name[2] == '\0')
 				continue;
+			if (!ctx.cfg.scan_hidden_path)
+				continue;
 		}
 		buf = malloc(strlen(path) + strlen(ent->d_name) + 2);
 		if (!buf) {