handle case where ~/.rvm/bin/rvm-prompt is not in path, so "which" can't find it

themes/crunch.zsh-theme

@@ -29,7 +29,7 @@ ZSH_THEME_GIT_PROMPT_DIRTY=" $CRUNCH_GIT_DIRTY_COLOR✗"
 
 # Our elements:
 CRUNCH_TIME_="$CRUNCH_BRACKET_COLOR{$CRUNCH_TIME_COLOR%T$CRUNCH_BRACKET_COLOR}%{$reset_color%}"
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   CRUNCH_RVM_="$CRUNCH_BRACKET_COLOR"["$CRUNCH_RVM_COLOR\${\$(~/.rvm/bin/rvm-prompt i v g)#ruby-}$CRUNCH_BRACKET_COLOR"]"%{$reset_color%}"
 else
   if which rbenv &> /dev/null; then

themes/dallas.zsh-theme

@@ -3,7 +3,7 @@
 # Grab the current date (%D) and time (%T) wrapped in {}: {%D %T}
 DALLAS_CURRENT_TIME_="%{$fg[white]%}{%{$fg[yellow]%}%D %T%{$fg[white]%}}%{$reset_color%}"
 # Grab the current version of ruby in use (via RVM): [ruby-1.8.7]
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   DALLAS_CURRENT_RUBY_="%{$fg[white]%}[%{$fg[magenta]%}\$(~/.rvm/bin/rvm-prompt i v)%{$fg[white]%}]%{$reset_color%}"
 else
   if which rbenv &> /dev/null; then

themes/macovsky-ruby.zsh-theme

 # ZSH Theme - Preview: http://gyazo.com/8becc8a7ed5ab54a0262a470555c3eed.png
 local return_code="%(?..%{$fg[red]%}%? ↵%{$reset_color%})"
 
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   PROMPT='%{$fg[green]%}%~%{$reset_color%} %{$fg[red]%}‹$(~/.rvm/bin/rvm-prompt i v)› %{$reset_color%} $(git_prompt_info)%{$reset_color%}%B$%b '
 else
   if which rbenv &> /dev/null; then

themes/macovsky.zsh-theme

 # ZSH Theme - Preview: http://gyazo.com/8becc8a7ed5ab54a0262a470555c3eed.png
 local return_code="%(?..%{$fg[red]%}%? ↵%{$reset_color%})"
 
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   PROMPT='%{$fg[green]%}%~%{$reset_color%} %{$fg[red]%}‹$(~/.rvm/bin/rvm-prompt i v)› %{$reset_color%} $(git_prompt_info)%{$reset_color%}%B$%b '
 else
   if which rbenv &> /dev/null; then

themes/superjarin.zsh-theme

 # Grab the current version of ruby in use (via RVM): [ruby-1.8.7]
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   JARIN_CURRENT_RUBY_="%{$fg[white]%}[%{$fg[red]%}\$(~/.rvm/bin/rvm-prompt i v)%{$fg[white]%}]%{$reset_color%}"
 else
   if which rbenv &> /dev/null; then

themes/zhann.zsh-theme

 PROMPT='%{$fg_bold[green]%}%p %{$fg[cyan]%}%c%{$fg_bold[blue]%}$(git_prompt_info)%{$fg_bold[blue]%} % %{$reset_color%}'
 
-if which rvm-prompt &> /dev/null; then
+if [ -e ~/.rvm/bin/rvm-prompt ]; then
   RPROMPT='%{$reset_color%} %{$fg[red]%}$(~/.rvm/bin/rvm-prompt i v g) %{$reset_color%}'
 else
   if which rbenv &> /dev/null; then