BUG: mpl fix to AutoDatFromatter to fix second/us-second formatters

revert part of #11770
xref: matplotlib/matplotlib#6365

closes #13131

The mistake in #11770 was missing that pandas had a 1/us not 1/s
scaled bucket.

doc/source/whatsnew/v0.18.2.txt

@@ -141,6 +141,7 @@ Bug Fixes
 - Bug in ``SparseDataFrame`` in which ``axis=None`` did not default to ``axis=0`` (:issue:`13048`)
 - Bug in ``SparseSeries`` and ``SparseDataFrame`` creation with ``object`` dtype may raise ``TypeError`` (:issue:`11633`)
 - Bug when passing a not-default-indexed ``Series`` as ``xerr`` or ``yerr`` in ``.plot()`` (:issue:`11858`)
+- Bug in matplotlib ``AutoDataFormatter``; this restores the second scaled formatting and re-adds micro-second scaled formatting (:issue:`13131`)
 
 
 - Bug in ``.groupby(..).resample(..)`` when the same object is called multiple times (:issue:`13174`)

pandas/tseries/converter.py

@@ -23,6 +23,24 @@
 from pandas.tseries.frequencies import FreqGroup
 from pandas.tseries.period import Period, PeriodIndex
 
+# constants
+HOURS_PER_DAY = 24.
+MIN_PER_HOUR = 60.
+SEC_PER_MIN = 60.
+
+SEC_PER_HOUR = SEC_PER_MIN * MIN_PER_HOUR
+SEC_PER_DAY = SEC_PER_HOUR * HOURS_PER_DAY
+
+MUSEC_PER_DAY = 1e6 * SEC_PER_DAY
+
+
+def _mpl_le_2_0_0():
+    try:
+        import matplotlib
+        return matplotlib.compare_versions('2.0.0', matplotlib.__version__)
+    except ImportError:
+        return False
+
 
 def register():
     units.registry[lib.Timestamp] = DatetimeConverter()
@@ -221,6 +239,13 @@ def __init__(self, locator, tz=None, defaultfmt='%Y-%m-%d'):
         if self._tz is dates.UTC:
             self._tz._utcoffset = self._tz.utcoffset(None)
 
+        # For mpl > 2.0 the format strings are controlled via rcparams
+        # so do not mess with them.  For mpl < 2.0 change the second
+        # break point and add a musec break point
+        if _mpl_le_2_0_0():
+            self.scaled[1. / SEC_PER_DAY] = '%H:%M:%S'
+            self.scaled[1. / MUSEC_PER_DAY] = '%H:%M:%S.%f'
+
 
 class PandasAutoDateLocator(dates.AutoDateLocator):