Port over fix to bug 2662 from master branch (leaking file descriptors)

PTYTask.m

@@ -664,6 +664,12 @@ static void reapchild(int n)
         sigaddset(&signals, SIGPIPE);
         sigprocmask(SIG_UNBLOCK, &signals, NULL);
+        // Apple opens files without the close-on-exec flag (e.g., Extras2.rsrc).
+        // See issue 2662.
+        for (int j = 3; j < getdtablesize(); j++) {
+          close(j);
+        }
+
         chdir(initialPwd);
         // Sub in our environ for the existing one. Since Mac OS doesn't have execvpe, this hack
         // does the job.
@@ -693,6 +699,9 @@ static void reapchild(int n)
     }
     free(newEnviron);
+    // Make sure the master side of the pty is closed on future exec() calls.
+    fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
+
     tty = [[NSString stringWithUTF8String:theTtyname] retain];
     NSParameterAssert(tty != nil);