Make the startup script call exec instead of forking a child.
Make the startup script call exec instead of forking a child.

This change makes it easier to use node-fibers with node-supervisor,
or any other tool that monitors the health of the node process.  It
also results in a simpler process structure, and makes "node-fibers"
closer to a true drop-in replacement for "node".

palsmadal/node-fibers,meteor/node-fibers,meteor/node-fibers,tempbottle/node-fibers,Icenium/node-fibers,rydn/node-fibers,rydn/node-fibers,metamatt/node-fibers,rydn/node-fibers,cgvarela/node-fibers,laverdet/node-fibers,metamatt/node-fibers,spookd/node-fibers,xolvio/node-fibers,palsmadal/node-fibers,tempbottle/node-fibers,d3m3vilurr/node-fibers,lzpfmh/node-fibers,Sanjo/node-fibers,tempbottle/node-fibers,pjump/node-fibers,dut3062796s/node-fibers,rydn/node-fibers,tempbottle/node-fibers,laverdet/node-fibers,Icenium/node-fibers,pjump/node-fibers,lzpfmh/node-fibers,meteor/node-fibers,meteor/node-fibers,d3m3vilurr/node-fibers,Icenium/node-fibers,xolvio/node-fibers,lzpfmh/node-fibers,spookd/node-fibers,d3m3vilurr/node-fibers,laverdet/node-fibers,cgvarela/node-fibers,Sanjo/node-fibers,dut3062796s/node-fibers,metamatt/node-fibers,metamatt/node-fibers,spookd/node-fibers,spookd/node-fibers,cgvarela/node-fibers,palsmadal/node-fibers,xolvio/node-fibers,palsmadal/node-fibers,dut3062796s/node-fibers,lzpfmh/node-fibers,Sanjo/node-fibers,Icenium/node-fibers,Sanjo/node-fibers,pjump/node-fibers,dut3062796s/node-fibers,xolvio/node-fibers,cgvarela/node-fibers,laverdet/node-fibers,d3m3vilurr/node-fibers,pjump/node-fibers