ExhaustiveSearchCoveringRadius( code )
ExhaustiveSearchCoveringRadius does an exhaustive search to find the covering
radius of code.
Every time a coset leader of a coset with weight w is found,
the function tries to find a coset leader of a coset with weight w+1.
It does this by enumerating all words of weight w+1, and checking
whether a word is a coset leader.
The start weight is the current known lower bound on the
covering radius.
GAP 3.4.4