bug#42346: Support Xcursor in Xlib

[Ivan Kozlov]

libX11 contains support for runtime loading of libXcursor. Without this 
support, programs that use Xlib’s mouse cursor routines, such as XTerm, do not 
follow the mouse cursor theme as determined by the Xcursor.theme resource and 
XCURSOR_THEME environment variable. This is in fact very noticeable and 
annoying.

How to reproduce:
1. Start XTerm.
2. Notice that the mouse cursor looks totally different from everything else. 
XTerm uses several mouse cursors: one for the text area, one for scrollbar, one 
for the menus, and they all stand out like a sore thumb.
3. Put libxcursor into LD_LIBRARY_PATH and start XTerm again.
4. Notice that the Xcursor theme is honoured.

This probably cannot be resolved by referencing libXcursor in libX11 because 
that would introduce a circular dependency.

The best solution I can think of is merging the libxcursor package into libx11. 
It is essentially a plugin.