Update the servo branch with changes from upstream and to build in Servo

These changes:
1) Pull in updates from upstream
2) Add a Makefile.servo.in file with the Servo-specific makefile rules
3) Adjust our old configure file to point at Makefile.servo.in instead of Makefile.in

Down the road, we may want to switch to configure-servo so that we can restore the upstream configure script (which we currently are shadowing/ignoring).

r? @metajack