#68 long lines with -wrap none. fixes

[James Bonfield]

Long lines (eg 10,000 characters) that are displayed
with -wrap none demonstrate a variety of bugs.

Firstly display is slow (more noticable with really
long lines) and secondly the tag colours, 3d bevels,
and the text itself is often displayed incorrectly.

The source of all of these bugs is 16-bit limitations
in the coordinates for X11. The patch adds in a
variety of add-hoc manual clipping in order to keep
coordinates within the 16-bit space.

Note that the same bugs also occur on windows due to
the 16-bit code in the xlib translation layer (eg
XSegment, XPoint and XRectangle structure
definitions).

This patch was implemented and tested with 8.3.1, but
the fix has been added into files checked out from
cvs HEAD today (10th April 2002), although they have
not been tested with that version. (I doubt there'll
be any difference as the files changed have not had
may edits.)

[James Bonfield]

patch against HEAD

[Jeffrey Hobbs]

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patched as attached for 8.4a5 head.

[Jeffrey Hobbs]

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I'm reopening this because while it does appear to correct
Unix, it does not correct the Windows side.

[Vince Darley]

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This is also a problem on MacOS X.

[Jeffrey Hobbs]

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Had to revert the XGetGeometry call in
tkUnixFont.c:Tk_DrawChars because users noted that it
makes an X server call for every string drawn, dramatically
reducing Tk performance on remote clients.