Modify win32 text width(ucs) function to handle surrogate pairs.

This now correctly measures glyphs whose codepoint requires a surrogate pair to represent it in UTF16.

NOTE 1: This code makes any UCS point > 0xFFFF a "special case" and measures it explicitly, rather than using the lookup table. This "explicit measure" may be slow, but actually seems OK in my tests, so far.
The lookup table still covers the basic multilingual plane and is used for any glyph <= 0xFFFF as before, so the behaviour for most existing bodies of text is unchanged.

This code also retains the historical behaviour under Win32 whereby strings are measured char-by-char rather than as a whole string - again this is intended to retain compatability with existing implementations.

It is proposed that we should move towards measuring entire strings in the future as this is conceivably more efficient and certainly more consistent - rendering is now largely done "string as a whole" so we ought to measure in that way too; though to date the differences seem tiny, as evdienced by the text rendering page of the unittest example.

NOTE 2: This does not fix the *rendering* of surrogate pairs under XP, which still seems to be broken. I suspect that TextOutW() may genuinely broken under XP, as it works fine on Vista, and it is not just my code that seems broken, other non-fltk programs exhibit the same aberrant behaviour. Measuring of surrogate pairs appears to work correctly though...
Maybe we are using TextOutW() wrongly?




git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@8580 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

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