cmPrefs.h: Update comments

cmPrefs.h

@@ -41,6 +41,9 @@ extern "C" {
   // Set 'fnName' to NULL to use cmFsAppName() as the pref file name.
   // Set 'fnExt' to NULL to use '.js' as the pref file extension.
   // 'cbFunc'  and 'cbDataPtr' are optional in both versions.
+  // 'pathPrefixStr' (optional) provides a prefix to be added to 
+  // the path of each preference variable. This can be used to separate
+  // preference data from other data in the preference file.
   cmPrRC_t cmPrefsInit(   cmCtx_t* ctx, cmPrH_t* hp, const cmChar_t* fnName, const cmChar_t* fnExt, cmPrefsOnChangeFunc_t cbFunc, void* cbDataPtr, const cmChar_t* pathPrefixStr );
   cmPrRC_t cmPrefsInitialize( cmCtx_t* ctx, cmPrH_t* hp, const cmChar_t* fn, cmPrefsOnChangeFunc_t cbFunc, void* cbDataPtr, const cmChar_t* pathPrefixStr);
   cmPrRC_t cmPrefsFinalize(   cmPrH_t* hp );