fuse: allow entering username and password via stdin

- when either username or password are not specified via commandline
   arguments or configuration file, ask them on standard input
 - unify function to read username and password
 - move function to read username and password from mfshell to
   utils/strings.c
 - remove commented cruft from utils/strings.c

utils/strings.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2013 Bryan Christ <bryan.christ@mediafire.com>
+ *               2014 Johannes Schauer <j.schauer@email.de>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2, as published by
@@ -19,6 +20,8 @@
 #ifndef _STR_TOOLS_H_
 #define _STR_TOOLS_H_
 
+#include <stdbool.h>
+
 char           *strdup_printf(char *fmt, ...);
 
 char           *strdup_join(char *string1, char *string2);
@@ -28,8 +31,6 @@ char           *strdup_subst(char *string, char *str_old, char *str_new,
 
 void            string_chomp(char *string);
 
-// void        string_strip_head(char *string,char c);
-
-// void        string_strip_tail(char *string,char c);
+char           *string_line_from_stdin(bool hide);
 
 #endif