Build hook: Pass the timeout to the remote builder

Note that this will only work if the client has a very recent Nix
version (post 15e1b2c223), otherwise the
--option flag will just be ignored.

Fixes #50.

scripts/build-remote.pl.in

@@ -46,8 +46,7 @@ sub all { $_ || return 0 for @_; 1 }
 # Initialisation.
 my $loadIncreased = 0;
 
-my ($localSystem, $maxSilentTime, $printBuildTrace) = @ARGV;
-$maxSilentTime = 0 unless defined $maxSilentTime;
+my ($localSystem, $maxSilentTime, $printBuildTrace, $buildTimeout) = @ARGV;
 
 my $currentLoad = $ENV{"NIX_CURRENT_LOAD"};
 my $conf = $ENV{"NIX_REMOTE_SYSTEMS"};
@@ -258,7 +257,9 @@ close UPLOADLOCK;
 
 
 # Perform the build.
-my $buildFlags = "--max-silent-time $maxSilentTime --fallback --add-root $rootsDir/\$PPID.out --option verbosity 0";
+my $buildFlags =
+    "--max-silent-time $maxSilentTime --option build-timeout $buildTimeout "
+    . "--fallback --add-root $rootsDir/\$PPID.out --option verbosity 0";
 
 # We let the remote side kill its process group when the connection is
 # closed unexpectedly.  This is necessary to ensure that no processes