Update code to compile against XCB util-wm >= 0.3.8

Update code to compile against XCB util-wm >= 0.3.8
XCB ICCCM public functions, types and macros are now prefixed.
A temporary fix has been added for OpenBSD.  Needs improvement.

Resolve a variable naming conflict.

Set num_screens in unmap_all.

In workaround(), utf8_string should be netwmname, not netwmcheck.

Initialize some uninitialized pointers.

Update debug printf format to reflect new xcb variable types.

Vacuum up whitespace.

Add XCB libs to linux Makefile