Remove cyclic dependency on thud_assert

Remove calls to thud_assert from within itself and functions it calls.
Fix '*' key transfer in thud_arr_print/parse

Prepend each printed value with '=' in thud_arr_print, expect it in
thud_arr_parse, to fix transfer of trailing empty values, instead of
terminating the output with '*' key.

This fixes transferring arrays containing '*' keys.