e2fsck: clean up assertions in dict.c

e2fsck: clean up assertions in dict.c

The C preprocessing symbol NDEBUG is also defined (differently) by
Android's build files, and this was causing compilation failures.  So
change assert() to dict_assert() and manually define it instead of
relying on the NDEBUG and <assert.h> semantics.

Also make sure the necessary debugging functions are available is
DICT_NODEBUG is not defined, so that dict.c will correctly build with
and without DICT_NODEBUG.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>