Refactored into chart specific methods.

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branch : 1.8
Refactored to use a property only.

--HG--
branch : 1.8
Whitespace

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branch : 1.8
xml:space=preserve is not required for workbooks and worksheets
XMLTidied some files.

--HG--
branch : 1.8
Reorganised multiline imports

--HG--
branch : 1.8
Refactored multiline import

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branch : 1.8
Empty cells are coerced to having u““ as a default value and data_type. This makes a mess when trying to infer a single data type for a series of values, some of which may be None, so cells with value = u““ are now ignored.

--HG--
branch : 1.8
Test marked to fail. c:Legend is no longer a valid child of c:ser

--HG--
branch : 1.8