Use roken_get_*() instead of getpwuuid()

Using non-reentrant getpwuid() (or getpwnam(), or getspnam())  can be
dangerous.  We had a report of a login application / PAM that calls
those, and Heimdal, by calling them too, clobbered the cached struct
passwd used by the login app / PAM.

lib/hx509/softp11.c

@@ -819,45 +819,25 @@ static char *
 get_config_file_for_user(void)
 {
     char *fn;
-
-#ifndef _WIN32
-    char *home;
     int ret;
 
     fn = secure_getenv("SOFTPKCS11RC");
     if (fn)
         fn = strdup(fn);
-    home = secure_getenv("HOME");
-    if (fn == NULL && home == NULL) {
-        struct passwd *pw = getpwuid(getuid());
-        if(pw != NULL)
-            home = pw->pw_dir;
-    }
     if (fn == NULL) {
+        char homebuf[MAX_PATH];
+        const char *home = roken_get_appdatadir(homebuf, sizeof(homebuf));
+
         if (home) {
             ret = asprintf(&fn, "%s/.soft-token.rc", home);
 	    if (ret == -1)
 		fn = NULL;
-        } else
+        } else {
+#ifndef WIN32
             fn = strdup("/etc/soft-token.rc");
+#endif
+        }
     }
-#else  /* Windows */
-
-    char appdatafolder[MAX_PATH];
-
-    fn = getenv("SOFTPKCS11RC");
-
-    /* Retrieve the roaming AppData folder for the current user.  The
-       current user is the user account represented by the current
-       thread token. */
-
-    if (fn == NULL &&
-        SUCCEEDED(SHGetFolderPath(NULL, CSIDL_APPDATA, NULL, SHGFP_TYPE_CURRENT, appdatafolder))) {
-
-        asprintf(&fn, "%s\\.soft-token.rc", appdatafolder);
-    }
-
-#endif  /* _WIN32 */
 
     return fn;
 }