Implement --debug, used to dump the first 'existing_file'.

diff --git a/pl.py b/pl.py
index 3f6eaa2..268dcd8 100755
--- a/pl.py
+++ b/pl.py
@@ -60,12 +60,13 @@ MUSIC_EXT = [
    ]

 REPLACE_MARKER = '** please try to replace ** '
+DEBUG_FORMAT = '** DEBUG INFO: %s **'

 def main():
     valid_actions = ['check', 'create']
     parser = optparse.OptionParser()
     parser.usage = "%prog [OPTIONS...] ACTION PLAYLIST [OTHER_PLAYLIST]\n" + \
-       "   [-defhitV] [--delete] [--error-stop] [--fix] [--ignore-case]\n" + \
+       "   [-dDefhitV] [--debug] [--delete] [--error-stop] [--fix] [--ignore-case]\n" + \
        "   [-n NB_SUGGS] [-p PREFIX] [-s SCORE] [-t TARGET]\n" + \
        "   [--prefix PREFIX] [--score SCORE] [--target TARGET]\n" + \
        "   [--help] [--version]\n" + \
@@ -85,7 +86,10 @@ def main():
     parser.add_option('-a', '--auto-fix', default=False,
        action='store_true', dest='auto_fix',
        help="check - change a missing entry to the first suggestion")
-    parser.add_option('-d', '--delete', default=False,
+    parser.add_option('-d', '--debug', default=False,
+       action='store_true', dest='debug',
+       help="print some info while running")
+    parser.add_option('-D', '--delete', default=False,
        action='store_true', dest='delete',
        help="check - delete entries that were not found")
     parser.add_option('-e', '--error-stop', default=False,
@@ -157,6 +161,9 @@ def main():
         bad_playlists = []
         # build the list of present files
         existing_files = music_files_list(options.target, options.prefix)
+        if options.debug:
+            debug_info = "First file found: %s." % existing_files[0]
+            print DEBUG_FORMAT % debug_info
         if options.ignore_case:
             existing_files = [elt.lower() for elt in existing_files]
         for playlist in playlists: