ENH: Use xlrd >=0.9.0 for both xls/xlsx, sidesteps GH1629
Ssers with xlrd<0.9 will get an error message.
unlike openpyxl, xlrd parse() leaves type inferencing to
TextReader, which looks at the first values only, but this
was already the behaviour for .xls files, so small price to pay.

Removed much code duplication, and xlrd 0.9.0 added py3
support (courtesy of @takluyver, Thanks!), though that's not
tested yet.

Also, closes #1629
