Another POC initdb patch

Hi all,

In addition to Tom's patch, this patch asks tuning parameters right away,
while doing initdb. I have also changed the notice displayed after initdb is
done.

Just an attempt to make defaults user friendly. I would also like to add other
paramters to this approach, like fsync and random_page_cost but first I
thought others should have look at these.

And one more thing, can we get all the parameters in postgresql.conf to follow
similar units? Some settings aer in 8KB pages, some in bytes etc. Can we haev
all of them to follow say MB or KB?

I tried but guc.h and guc.c were bit too much to be gulped at one go. I will
try again.

Shridhar