patch: fix external ed invocation (#904)

* patch: fix external ed invocation

* This version of patch first attempts to process an ed diff by running an external ed command, then falls back to processing the ed commands directly
* I noticed the external ed code was always failing but I didn't debug it until now
* Problem1: SIGCHLD happens normally when ed exits but it was being treated as an error (removing signal handlers fixes it)
* Problem2: write command sent to ed was not terminated by a newline, so ed would never run the command
* Problem3: after writing to o_file, the offset of filehandle $out was at byte 26, so the test line comparison wasn't correct
* With this patch I can process a simple ed diff on Linux without the code reaching PLAN_J

* revert pipe argument list conversion to scalar

bin/patch

@@ -24,7 +24,7 @@ use constant EX_SUCCESS => 0;
 use constant EX_REJECTS => 1;
 use constant EX_FAILURE => 2;
 
-my $VERSION = '0.30';
+my $VERSION = '0.31';
 
 $|++;
 
@@ -912,16 +912,16 @@ sub apply {
 
     # Pipe to ed.
     eval {
-        local $SIG{PIPE} = sub { die 'Pipe broke...' };
-        local $SIG{CHLD} = sub { die 'Bad child...' };
-        open ED, '|-', qw(ed - -s), $self->{i_file} or die "Couldn't fork ed: $!";
+        open ED, '|-', 'ed', '-s', $self->{'i_file'} or die "Couldn't fork ed: $!";
         print ED map @$_, @cmd               or die "Couldn't print ed: $!";
-        print ED "1,\$w $self->{o_file}"     or die "Couldn't print ed: $!";
+        print ED "wq $self->{o_file}\n"     or die "Couldn't print ed: $!";
         close ED                             or die "Couldn't close ed: $?";
     };
 
     # Did pipe to ed work?
-    unless ($@ or <$out> ne $magic) {
+    seek($out, 0, 0)  or throw("Couldn't seek OUT: $!");
+    my $testline = <$out>;
+    if (!$@ && $testline ne $magic) {
         $self->note("Hunk #$self->{hunk} succeeded at 1.\n");
         return 1;
     }