Construct PS1 string once

Rather than re-constructing PS1 each time the prompt is called, it can
be built once. The portions of it which call functions are still called,
so there is no drawback to setting it and forgetting it.

src/.bashrc

@@ -453,31 +453,10 @@ function _ps1_color {
 	echo -e "$color"
 }
 
-# PS1 builder and history appender
-# see _ps1_color for color reference for each PS1 segment
-# Note: all non-printing sequences must be surrounded by \[ \]
-# Note: bash PS1 title can only reference variables eg. $PWD
-#       (calling functions causes errors in title eg. pwd)
+# history appender
 function _bashrc_prompt_command {
-	# this must run first to capture exit status
-	local EXIT="$?"
-
 	# append last command to history
 	history -a
-
-	# set window title
-	# format:  $PWD; $?=#
-	PS1='\[\e]0;'"$PWD"'; \$?='"$EXIT"'\007\]'
-	PS1+='\n'
-
-	# set first line
-	# format:  [user@host path] (git branch)
-	PS1+='\[$(_ps1_color bracket)\][\[$(_ps1_color user)\]\u\[$(_ps1_color @)\]@\[$(_ps1_color host)\]\[$(hostname -f 2>/dev/null || hostname)\] \[$(_ps1_color path)\]\w\[$(_ps1_color bracket)\]]\[$(_ps1_color branch)\]\[$(__git_ps1 2>/dev/null)\]\[$(_ps1_color prompt)\]'
-	PS1+='\n'
-
-	# set second line
-	# format:  $
-	PS1+='\[$(_ps1_color preprompt)\]\$\[$(_ps1_color prompt)\] '
 }
 
 # exit function
@@ -628,6 +607,25 @@ _bashrc_ssh-add-keys
 # echo motd
 _bashrc_motd
 
-# sets PS1, appends to history
-PROMPT_COMMAND="_bashrc_prompt_command"
+### set PS1/PS2, appends to history
+
+# see _ps1_color for color reference for each PS1 segment
+# Note: all non-printing sequences must be surrounded by \[ \]
+# Note: bash PS1 title can only reference variables eg. $PWD
+#       (calling functions causes errors in title eg. pwd)
+
+# set window title
+# format:  $PWD; $?=#
+PS1='\[\e]0;'"$PWD"'; \$?=$?\007\]'
+PS1+='\n'
+
+# set first line
+# format:  [user@host path] (git branch)
+PS1+='\[$(_ps1_color bracket)\][\[$(_ps1_color user)\]\u\[$(_ps1_color @)\]@\[$(_ps1_color host)\]\[$(hostname -f 2>/dev/null || hostname)\] \[$(_ps1_color path)\]\w\[$(_ps1_color bracket)\]]\[$(_ps1_color branch)\]\[$(__git_ps1 2>/dev/null)\]\[$(_ps1_color prompt)\]'
+PS1+='\n'
+
+# set second line
+# format:  $
+PS1+='\[$(_ps1_color preprompt)\]\$\[$(_ps1_color prompt)\] '
 PS2='\[$(_ps1_color preprompt)\]>\[$(_ps1_color prompt)\] '
+PROMPT_COMMAND="_bashrc_prompt_command"