error in common na_values definition
Note for  0.14.1: need to add back `#N/A N/A` to na_values defaults

in pandas 0.12

i found a little bug:

this:
_NA_VALUES = set(['-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN',
                 '#N/A N/A', 'NA', '#NA', 'NULL', 'NaN',
                 'nan', ''])

must be:
_NA_VALUES = set(['-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN',
                 '#N/A','N/A', 'NA', '#NA', 'NULL', 'NaN',
                 'nan', ''])

thank you
Glauco
