Build fixes.

Build fixes.

- atspi-application.h makes use of DBusConnection* .
- -Werror-implicit-function-declaration doesn't contain an equal sign in
  my copy of gcc, and is gcc specific.
- The default behaviour of AC_CHECK_LIB glib-2.0 is to add -lglib-2.0 to
  LIBS which can then cause the search for a dlopen function to fail
  because the flags to find libglib aren't included. Solution is to
  tell AC_CHECK_LIB to do nothing(!)