Reduce some data dependencies between X calls

Reduce some data dependencies between X calls

Gains nothing in the traditional-Xlib code, but more closely aligns
with how the XCB version will work.

* src/xfns.c (x_real_pos_and_offsets): When translating coordinates,
send coordinates (0,0) to the X server and add in the real coordinates
after getting the response.  Move XGetGeometry for outer window inside
error-trapping block.  Use DPY variable more, since it's available.