Resolve "make error messages more descriptive"

Closes #8

gridded_glm/libexec/_minute_gridder.py

@@ -159,9 +159,6 @@ def grid_setup(args, work_dir=os.getcwd()):
 
     try:
         start_time, end_time = get_start_end(args.filenames)
-    except ValueError:
-        log.error("Non-standard filenames provided, use --start and --end to specify data times.")
-        raise
     except:
         log.error("Could not parse start & end times from one or more of the files provided.")
         exit(1)