line from ruler to current mouse position if polar distance

[Petr M. <mi...@ph...>]

Can you please test this patch:
https://sourceforge.net/tracker/?func=detail&atid=302055&aid=1520821&group_id=2055

The patch completes the functionality of the ruler-cursor visualizatin in 
"polar distance" (=distance, angle, slope) mode.


Patch description:
This patch draws a line from ruler to current mouse
cursor when ruler is visible (hotkey 'r') and polar
distance is displayed in the status bar (hotkey '5').

This implements calls set_cursor(flag,...) for flag=-3
and -4. Currently implemented for x11 and windows
terminals; implementation for wxt and pm is welcome.

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PM