[UPDATE][SCRIPT] Use expansion for PROMPT_COMMAND

It seems like the idiomatic way to update $PROMPT_COMMAND is to use
variable expansion to add a semi-colon and a space before the command
we're adding.

I also switched from prepending my commands to appending them, which
allows overriding behaviour, such as terminal titles which could be set
from system files.

scripts/localrc

@@ -110,7 +110,7 @@ function __source_localrc_files() {
 # Execute this command every time
 if [ -n "$BASH_VERSION" ]; then
     [ -n "${DEBUG_LOCALRC+set}" ] && echo "Loaded Bash"
-    PROMPT_COMMAND="__source_localrc_files; $PROMPT_COMMAND"
+    PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND; }__source_localrc_files"
 elif [ -n "$ZSH_VERSION" ]; then
     [ -n "${DEBUG_LOCALRC+set}" ] && echo "Loaded Zsh"
     precmd_functions+=( __source_localrc_files)

scripts/term-title

@@ -36,7 +36,7 @@ __term_title_prompt_command() {
 
 case "$TERM" in
     xterm*|term_title*)
-        [ -n "$BASH_VERSION" ] && PROMPT_COMMAND="__term_title_prompt_command;$PROMPT_COMMAND"
+        [ -n "$BASH_VERSION" ] && PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND; }__term_title_prompt_command"
         [ -n "$ZSH_VERSION"  ] && precmd_functions+=(__term_title_prompt_command)
         ;;
 esac