fifo: add PID in default FIFO pipe filename (issue #1285)

This is to prevent two WeeChat using the same runtime directory to use the same
FIFO pipe.

src/plugins/fifo/fifo-command.c

@@ -102,8 +102,9 @@ fifo_command_init ()
            "\n"
            "FIFO pipe is used as remote control of WeeChat: you can send "
            "commands or text to the FIFO pipe from your shell.\n"
-           "By default the FIFO pipe is called weechat_fifo and saved in the "
-           "WeeChat runtime directory (see /debug dirs).\n"
+           "By default the FIFO pipe is called weechat_fifo_xxx (where xxx is "
+           "the WeeChat process id) and saved in the WeeChat runtime directory "
+           "(see /debug dirs).\n"
            "\n"
            "The expected format is one of:\n"
            "  plugin.buffer *text or command here\n"
@@ -111,7 +112,7 @@ fifo_command_init ()
            "\n"
            "For example to change your freenode nick:\n"
            "  echo 'irc.server.freenode */nick newnick' "
-           ">/run/user/1000/weechat/weechat_fifo\n"
+           ">/run/user/1000/weechat/weechat_fifo_12345\n"
            "\n"
            "Please read the user's guide for more info and examples.\n"
            "\n"

src/plugins/fifo/fifo-config.c

@@ -122,7 +122,7 @@ fifo_config_init ()
            "WeeChat PID can be used in path with ${info:pid} "
            "(path is evaluated, see function string_eval_path_home in "
            "plugin API reference)"),
-        NULL, 0, 0, "${weechat_runtime_dir}/weechat_fifo", NULL, 0,
+        NULL, 0, 0, "${weechat_runtime_dir}/weechat_fifo_${info:pid}", NULL, 0,
         NULL, NULL, NULL,
         fifo_config_change_file_path, NULL, NULL,
         NULL, NULL, NULL);