update error message for unspecified exceptions

- ask user to report unexpected errors, which usually indicate
  extractor failure
- handle OSErrors separately (permissions, disk full, etc)
- revert 30eef52

gallery_dl/job.py

@@ -56,15 +56,15 @@ class Job():
             log.error("HTTP request failed:\n%s", exc)
         except exception.StopExtraction:
             pass
+        except OSError as exc:
+            log.error("Unable to download data: %s", exc)
         except Exception as exc:
-            msg = "An unexpected error occurred:"
-            try:
-                err = ": ".join(exc.args[0].reason.args[0].split(": ")[1:])
-                log.error("%s: %s - %s", msg, exc.__class__.__name__, err)
-                return
-            except Exception:
-                pass
-            log.error(msg, exc_info=True)
+            log.error(("An unexpected error occurred: %s - %s. "
+                       "Please run gallery-dl again with the --verbose flag, "
+                       "copy its output and report this issue on "
+                       "https://github.com/mikf/gallery-dl/issues ."),
+                      exc.__class__.__name__, exc)
+            log.debug("Traceback", exc_info=True)
 
     def dispatch(self, msg):
         """Call the appropriate message handler"""