OverflowError when trying to use date/times
Hello, I have an issue that I posted to SO that wasn't able to be resolved there, seems like it should be straightforward. 

https://stackoverflow.com/questions/47227268/pandas-dataset-overflowerror-when-trying-to-use-datetime-data

I have since hardcoded in some sample data to ease error reproduction:

```
import datetime
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import matplotlib.cbook as cbook
import pandas
import StringIO

##f = open(r'clean data.csv')
##
###Make a string buffer and read in the CSV file while stripping \x00's
##output = StringIO.StringIO()
##for x in f.readlines():
##    output.write(x.replace('\x00',''))
##
###Close out input file
##f.close()
##
###Set position back to start for pandas to read
##output.seek(0)

datain = '''Time,101 <Stuff1> (C),102 <Stuff2> (C),103 <Stuff3> (C),104 <Stuff4> (C),107 <Stuff7> (C),108 <Air> (C)
8/25/2017 14:54,20.727,20.897,20.955,21.025,21.064,21.216
8/25/2017 14:55,20.851,20.953,21.025,21.055,21.1,21.264
8/25/2017 14:56,20.808,20.956,21.018,21.037,21.101,21.282
8/25/2017 14:57,20.799,20.944,20.99,21.029,21.095,21.189
8/25/2017 14:58,-9.824,21.006,21.026,21.064,21.093,21.218'''

output = StringIO.StringIO()
for x in datain.split('\n'):
    output.write(x+'\n')
output.seek(0)

#, skiprows=38
df = pandas.read_csv(output, parse_dates=['Time'], index_col="Time")

fig, ax = plt.subplots()
ax.xaxis.set_major_locator(mdates.DayLocator())
ax.format_xdata = mdates.DateFormatter('%Y-%m-%d')
ax.plot(df.index,df['108 <Air> (C)'])
fig.autofmt_xdate()
plt.show()
```

Result:
```
Traceback (most recent call last):
  File "C:\Users\awasilen\Desktop\graph.py", line 41, in <module>
    fig.autofmt_xdate()
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 491, in autofmt_xdate
    for label in self.axes[0].get_xticklabels(which=which):
  File "C:\Python27\lib\site-packages\matplotlib\axes\_base.py", line 3054, in get_xticklabels
    which=which))
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 1234, in get_ticklabels
    return self.get_majorticklabels()
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 1188, in get_majorticklabels
    ticks = self.get_major_ticks()
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 1339, in get_major_ticks
    numticks = len(self.get_major_locator()())
  File "C:\Python27\lib\site-packages\matplotlib\dates.py", line 871, in __call__
    dmin, dmax = self.viewlim_to_dt()
  File "C:\Python27\lib\site-packages\matplotlib\dates.py", line 832, in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "C:\Python27\lib\site-packages\matplotlib\dates.py", line 441, in num2date
    return _from_ordinalf(x, tz)
  File "C:\Python27\lib\site-packages\matplotlib\dates.py", line 256, in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix).replace(tzinfo=UTC)
OverflowError: Python int too large to convert to C long
```