Printing MultiIndex DataFrame header should be more compact

[sam-s]

MultiIndex DataFrame header is poorly aligned:

>>> pd.DataFrame({("extra very long top level name","Z"):[1,2,3],
                  ("extra very long top level name","longish second level name"):[4,5,6]})
  extra very long top level name                          
                               Z longish second level name
0                              1                         4
1                              2                         5
2                              3                         6

It would be more compact and readable if the first column of the second level did not try to align with the first level:

  extra very long top level name                          
     Z longish second level name
0    1                         4
1    2                         5
2    3                         6