Add back prompt_pwd to solve empty output problem

..by not manipulating path at all if we do not have
the tools to do so.

Tag changes with better comments.

share/config.fish

@@ -21,9 +21,15 @@ if status --is-interactive
 	# Existance of string is a good pre-2.3.0 check. Could also check $FISH_VERSION in the future.
 	# This is a "launch", not an issue caused by autoloading during upgrades.
 	if not contains "string" (builtin -n)
-		# the string.fish message to `exec` will probably not help here, so this will that.
 		set -g __is_launched_without_string 1
 
+		# XXX nostring - fix old fish binaries with no string builtin.
+		# With fish 2.2.0, these newer scritps are going to later force on 24-bit color due
+		# to changes to in behavior with conditionals. Let's show a public serivec announcement
+		# before skipping the 24bit opportunity. The user has seemingly explicitly launched an old
+		# fish with too-new scripts installed.
+		# Remove this when it's safe to upgrade fish and we've solved fish-script conflicts. 
+
 		set_color --bold
 		echo "You appear to be trying to launch an old fish binary with newer scripts "
 		echo "installed into" (set_color --underline)"$__fish_datadir" 

share/functions/__fish_config_interactive.fish

@@ -167,7 +167,6 @@ function __fish_config_interactive -d "Initializations that should be performed
 		commandline -f repaint
 	end
 
-
 	# Notify vte-based terminals when $PWD changes (issue #906)
 	if test "$VTE_VERSION" -ge 3405 -o "$TERM_PROGRAM" = "Apple_Terminal"
 		function __update_vte_cwd --on-variable PWD --description 'Notify VTE of change to $PWD'

share/functions/prompt_pwd.fish

@@ -1,12 +1,19 @@
 function prompt_pwd --description "Print the current working directory, shortened to fit the prompt"
-	set -q argv[1]; and switch $argv[1]
+    set -q argv[1]
+    and switch $argv[1]
         case -h --help
             __fish_print_help prompt_pwd
             return 0
     end
+    if set -q $__is_launched_without_string
+        # There is no `string' builtin - do something sensible. XXX nostring
+        echo $PWD
+        return 0
+    end
 
     # This allows overriding fish_prompt_pwd_dir_length from the outside (global or universal) without leaking it
-	set -q fish_prompt_pwd_dir_length; or set -l fish_prompt_pwd_dir_length 1
+    set -q fish_prompt_pwd_dir_length
+    or set -l fish_prompt_pwd_dir_length 1
 
     # Replace $HOME with "~"
     set realhome ~

share/functions/string.fish

@@ -1,4 +1,5 @@
 if not contains string (builtin -n)
+	# XXX nostring
 	function string
 		if not set -q __is_launched_without_string
 			if status --is-interactive