Truly synchronous require()

This is to reduce our dependency on wait(). For some reason this patch
affects the timer test:

  % ./node test/mjsunit/test-timers.js
  diff: 989
  diff: 989
  diff: 1989
  diff: 2989

Previously it showed:

  % ./node test/mjsunit/test-timers.js
  diff: 1000
  diff: 1000
  diff: 2000
  diff: 3000

I'm not sure what caused this change, and it's rather disturbing. However I
want to remove wait() as soon as possible and so am pushing this patch
through.

The module loading code is becoming increasingly ugly - this patch has not
helped. A refactor needs to be done soon.