Fixed backwards compatibility with original progressbar library

Author: wolph

progressbar/widgets.py

@@ -272,6 +272,9 @@ class Timer(FormatLabel, TimeSensitiveWidgetBase):
     '''WidgetBase which displays the elapsed seconds.'''
 
     def __init__(self, format='Elapsed Time: %(elapsed)s', **kwargs):
+        if '%s' in format and '%(elapsed)s' not in format:
+            format = format.replace('%s', '%(elapsed)s')
+
         FormatLabel.__init__(self, format=format, **kwargs)
         TimeSensitiveWidgetBase.__init__(self, **kwargs)
 
@@ -373,6 +376,9 @@ def __init__(
             format_NA='ETA:      N/A',
             **kwargs):
 
+        if '%s' in format and '%(eta)s' not in format:
+            format = format.replace('%s', '%(eta)s')
+
         Timer.__init__(self, **kwargs)
         self.format_not_started = format_not_started
         self.format_finished = format_finished