local: Add file ext blacklist (fixes #516).

Adds a new local/scan_blacklist_extensions config value for controlling file
extensions to ignore.

docs/ext/local.rst

@@ -52,6 +52,10 @@ Configuration values
     Number of milliseconds before giving up scanning a file and moving on to
     the next file.
 
+.. confval:: local/scan_blacklist_extensions
+
+    File extensions to ignore when scanning the media directory.
+
 
 Usage
 =====

mopidy/backends/local/__init__.py

@@ -23,6 +23,7 @@ class Extension(ext.Extension):
         schema['tag_cache_file'] = config.Path()
         schema['scan_timeout'] = config.Integer(
             minimum=1000, maximum=1000*60*60)
+        schema['scan_blacklist_extensions'] = config.List(optional=True)
         return schema
 
     def validate_environment(self):

mopidy/backends/local/ext.conf

@@ -4,3 +4,9 @@ media_dir = $XDG_MUSIC_DIR
 playlists_dir = $XDG_DATA_DIR/mopidy/local/playlists
 tag_cache_file = $XDG_DATA_DIR/mopidy/local/tag_cache
 scan_timeout = 1000
+scan_blacklist_extensions =
+  .jpeg
+  .jpg
+  .png
+  .txt
+  .log

mopidy/scanner.py

@@ -71,6 +71,7 @@ def main():
     local_updater = updaters.values()[0](config)  # TODO: switch to actor?
 
     media_dir = config['local']['media_dir']
+    blacklist_extensions = config['local']['scan_blacklist_extensions']
 
     uris_library = set()
     uris_update = set()
@@ -92,6 +93,10 @@ def main():
 
     logging.info('Checking %s for new or modified tracks.', media_dir)
     for uri in path.find_uris(config['local']['media_dir']):
+        if os.path.splitext(path.uri_to_path(uri))[1] in blacklist_extensions:
+            logging.debug('Skipped %s: File extension blacklisted.', uri)
+            continue
+
         if uri not in uris_library:
             uris_update.add(uri)