Try harder to remove old run artefacts

First, recursively set the permissions to 0700 so that rmtree shouldn't
fail. Then, if rmtree does fail (i.e. if the directories still exist)
die and don't proceed with the run.

run_build.pl

@@ -485,8 +485,20 @@ BEGIN
 	exit(0);
 }
 
+my $installdir = "$buildroot/$branch/inst";
+
+# recursively fix any permissions that might stop us removing the directories
+# then remove old run artefacts if any, die if not possible
+my $fix_perms = sub { chmod 0700, $_; };
+File::Find::find( $fix_perms, "inst");
 rmtree("inst");
-rmtree("$pgsql") unless ($from_source && !$use_vpath);
+die "$installdir exists!" if -e "inst";
+unless ($from_source && !$use_vpath)
+{
+	File::Find::find($fix_perms, "$pgsql");
+	rmtree($pgsql);
+	die "$pgsql exists!" if -e $pgsql;
+}
 
 # we are OK to run if we get here
 $have_lock = 1;
@@ -522,7 +534,6 @@ BEGIN
 use vars qw($now);
 BEGIN { $now = time; }
 
-my $installdir = "$buildroot/$branch/inst";
 my $dbstarted;
 
 my $extraconf;