Bug 3034

Because of new perl.req script, new build dependencies can be discovered too late
for -bc.  Thus sometimes I want to change the stage to -bi.  I have to run
something like this:

buildreq --args="$(eval `grep -- -bc /usr/bin/buildreq | sed -e s,-bc,-bi,`; echo
"$RPMARG")" package.spec

Actually this can be an alias (buildreqi).  Anyway, I believe there should be an
easier way.

1) buildreq should be able to take its STAGE argument (-bc is the default)
2) buildreq should specially mark non-default STAGE invocation in specfile
comment, something like:
# Automatically added by buildreq on Mon Sep 22 2003 (-bi)
3) when run next time, buildreq should restore the STAGE argument from the
comment.

PS: "should" means "feature request" here.