pg_upgrade and system() return value

Can someone comment on the attached patch?  pg_upgrade was testing if
system() returned a non-zero value, while I am thinking I should be
adjusting system()'s return value with WEXITSTATUS().

Is there any possible bug in back branches just compariing system()'s
turn value to non-zero without calling WEXITSTATUS()?  I never saw a bug
related to this.  I am thinking of applying this just to git head.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +