Replace a duplicated test to see if we're in an SVN folder with a call to the 'in_svn' function.

plugins/svn/svn.plugin.zsh

 function svn_prompt_info {
-    if [[ -d .svn ]]; then
+    if [ in_svn ]; then
         echo "$ZSH_PROMPT_BASE_COLOR$ZSH_THEME_SVN_PROMPT_PREFIX\
 $ZSH_THEME_REPO_NAME_COLOR$(svn_get_repo_name)$ZSH_PROMPT_BASE_COLOR$ZSH_THEME_SVN_PROMPT_SUFFIX$ZSH_PROMPT_BASE_COLOR$(svn_dirty)$ZSH_PROMPT_BASE_COLOR"
     fi