GCC produces ODR error when including paths of the form './foo' and
'foo' in the same binary. Rather than managing duplication we just
universally pick the absolute form over the relative form.
calculating the hash should never need to throw; all error cases should
be detectable at construction time. we should panic if we detect such an
error.
this fixes a compilation warning
HARD vs SOFT assertions were never very well defined or supported.
Currently they just imply a level of functionality that isn't present;
it's better to remove them instead of expending the effort at this
point.
