isso/init: Log paths at start, error if not found

Fixes isso-comments#585

isso/__init__.py

@@ -43,7 +43,7 @@
 import logging
 import tempfile
 
-from os.path import dirname, join
+from os.path import abspath, dirname, exists, join
 from argparse import ArgumentParser
 from functools import partial, reduce
 
@@ -177,6 +177,9 @@ class App(Isso, uWSGIMixin):
 
     isso = App(conf)
 
+    logger.info("Using database at '%s'",
+                abspath(isso.conf.get('general', 'dbpath')))
+
     if not any(conf.getiter("general", "host")):
         logger.error("No website(s) configured, Isso won't work.")
         sys.exit(1)
@@ -238,6 +241,16 @@ def main():
     subparser.add_parser("run", help="run server")
 
     args = parser.parse_args()
+
+    if not args.conf:
+        logger.info("No configuration file specified. Using defaults.")
+    else:
+        if not exists(args.conf):
+            logger.error("Specified config '%s' does not exist! Exiting.",
+                         abspath(args.conf))
+            sys.exit(1)
+        logger.info("Using configuration file '%s'", abspath(args.conf))
+
     conf = config.load(config.default_file(), args.conf)
 
     if args.command == "import":