mouse event handling

Conflicts:
	src/support/geom/rust-geom
more mouse events
rust-glut static vars for mouse buttons
adding more mouse events
glut static vars
handle mouse_up, mouse_down, and click separately; pass specific button to script_task
Merge branch 'master' of git://github.com/pcwalton/servo
improved profiling metrics
test_slam_layout, a new layout perf test case
beginnings of element finding
Merge branch 'master' of git://github.com/pcwalton/servo
link following upon mouse click
reverted changes to makefile.in and mk/clean
comments added to placeholder code
refactored HitTestResponse handling of urls from elements into helper fn
profiler refactor
Add link following and refactor the profiler.
engine interface, script_task now has engine_chan for  requests
handle relative url's when clicking
Implement scrolling and better zooming