Fix trying to save zconfig_t to non-existant path
zconfig_chunk_save will now save the wole config (sub)tree instead of just one config entry
Whitespace fixes
Thread local storage on gcc uses __thread
Problem: _test methods are not consistent

CLASS RFC specifies void methods; if a test fails the code should
abort. There is no semantic for returning an error code. However
many of the classes used an int type for their test method.

Solution: change all those classes to use a void method.