add initial randr support and adjust xinerama support
Replace struct rect with xcb_rectangle_t
Add back the BAR_OFFSET adjustments to init()
Update bar.c
Handle randr screen change events.
minor whitespace cleanup
fix get_xinerama_outputs: don't use global num_screens here
Remove the screen adjust and move the xinerama init back into init(); the screen_adjust removes screens structs that could easily be referenced  erroneously later and they take up very little space. There's no point doing the xinerama init as a separate function as it won't get called again.
Clean up after removing screen_adjust removal.
Rebased branch to commit cc34dab of bar master.
Ported randr code to wip branch, plus some fixes.