double-buffer incompatible with xinerama

[jackmclrtz]

I would recommend/request that the double-buffering added to sawfish be configurable via .sawfishrc so that it can be disabled.

Reasoning:

I installed a fresh system on my workstation (Debian 9), which installed:

ii sawfish 1:1.11.90-1+b1 amd64 window manager for X11

Since I have four monitors, I have to enable xinerama, or else X is just painful. While this combination of sawfish with nvidia/xinerama worked fine before, with the new version of sawfish, the title bars disappeared and sawfish reports a lot of:

Xlib: extension "DOUBLE-BUFFER" missing on display ":0".

Reseraching this, I found that Xdbe is disabled when xinerama is enabled because they are incompatible. Since this version of sawfish now uses double buffering:

    - Add double buffering of frame parts to reduce flickering while
      redraw of frames.  [hans1024]

This means that sawfish won't work with xinerama.
I pulled the debian sources for sawfish, disabled Xdbe in ./configure and built. It now works fine.