Rename DONT_USE_WIN_LINE_METRICS to match the spec

The [OS/2 spec][1] uses the name USE_TYPO_METRICS, so using the same
name here is less confusing.

I tried to update the MakeOTFUserGuide as well, but I don't have all the fonts used so I did not regenerate the PDF (it would be nicer of the document used free fonts and non-binary file format).

[1]: http://www.microsoft.com/typography/otspec/os2.htm#fss