Fix some build warnings

- Redefinition of DBUS_EXPORT
- A whole lot of "misleading indentation" (which only appear in newer gcc)
- One unused static variable in util.c (alphabet, previously used for base64)
- "left shift by negative value" with the IS_END macro of libgnt. That macro is
"1 << 0" and expanded to "~1 << 0" in one place. So now it's "(1 << 0)"