Refactor title and "lastrv" setting

This likely breaks hostname setting when accessing via SSH, but:

 *  it's first version that is at least somehow readable,

 *  and also WE *MAY* have fixed the long-standing PITA escaping
    errors that we used to get in urxvt if BASH_COMMAND had backslashes
    in it!

dotfiles/bash/post.bashrc

@@ -49,44 +49,63 @@ export PS1=$(__bashum__mkps1)
 export PS2=$(__bashum__mkps2)
 
 
-__bashum__setup_prompt_command() {
+__bashum__set_title() {
+    #
+    # Show the currently running command in the terminal title:
+    #
+    # http://www.davidpashley.com/articles/xterm-titles-with-bash.html
+    #
+    case "$BASH_COMMAND" in
+        *\033]0*)
+            # The command is trying to set the title bar as well;
+            # this is most likely the execution of $PROMPT_COMMAND.
+            # In any case nested escapes confuse the terminal, so don't
+            # output them.
+            ;;
+        "")
+            echo -ne "\033]0;"
+            echo -n    "$(__bashum__lastrv)$(__bashum__mkhostid)${PWD/$HOME/\~}\$"
+            echo -ne "\007"
+            ;;
+        *)
+            echo -ne "\033]0;"
+            echo -n    "${BASH_COMMAND} ($(__bashum__mkhostid)${PWD/$HOME/\~})"
+            echo -ne "\007"
+            ;;
+    esac
+}
 
+__bashum__mkpc() {
+    #
+    # Compose PROMPT_COMMAND body
+    #
+    echo -n '__bashum__save_rv $?;'
     case "$TERM" in
-
         xterm*|rxvt*|screen*)
-            test -n "$SSH_CONNECTION" \
-             && __host_id="${HOSTNAME%%.*}:"      # i.e. a remote session
-            PROMPT_COMMAND='__bashum__save_rv $?; echo -ne "\033]0;$(__bashum__lastrv)$__host_id${PWD/$HOME/\~}\$\007"'
-
-            # Show the currently running command in the terminal title:
-            # http://www.davidpashley.com/articles/xterm-titles-with-bash.html
-            show_command_in_title_bar()
-            {
-                case "$BASH_COMMAND" in
-                    *\033]0*)
-                        # The command is trying to set the title bar as well;
-                        # this is most likely the execution of $PROMPT_COMMAND.
-                        # In any case nested escapes confuse the terminal, so don't
-                        # output them.
-                        ;;
-                    "")
-                        echo -ne "\033]0;$(__bashum__lastrv)$__host_id${PWD/$HOME/\~}\$\007"
-                        ;;
-                    *)
-                        echo -ne "\033]0;${BASH_COMMAND} ($__host_id${PWD/$HOME/\~})\007"
-                        ;;
-                esac
-            }
-            trap show_command_in_title_bar DEBUG
+            echo -n 'echo -ne "\033]0;'
+            echo -n   '$(__bashum__lastrv)'
+            echo -n   "$(__bashum__mkhostid)"
+            echo -n   '${PWD/$HOME/\~}'
+            echo -n   '\$'
+            echo -n '\007"'
             ;;
+    esac
+}
 
-        *)
-            PROMPT_COMMAND='__bashum__save_rv $?;'
-            ;;
+__bashum__mkhostid() {
+    test -n "$SSH_CONNECTION" || return
+    echo "__bashum__mkhostid(): HOSTNAME='$HOSTNAME'" >&2
+    echo"${HOSTNAME%%.*}:"
+}
 
+__bashum__setup_traps() {
+    case "$TERM" in
+        xterm*|rxvt*|screen*) trap __bashum__set_title DEBUG ;;
     esac
 }
 
-__bashum__setup_prompt_command
+__bashum__setup_traps
+
+PROMPT_COMMAND=$(__bashum__mkpc)
 
 tasknag