removing the exec() from doexec()

I'm planning on removing the exec from DoExec() and instead just
dispatch to the appropriate function.

I don't plan on any changes to the usage of "arguments" to this new
process, basically I'll just store them somewhere and then the forked
backend can process them.

Is there anything I should keep in mind?  I'd like this to eventually
be integrated into the source tree -- any particular reason why we use
exec() when we're just re-invoking the same binary?

p.s. this is so my ssl patch doesn't have to negotiate twice -- very expensive