Assert-SameFile

This script automates one typical test scenario, it compares the sample and
result files and performs copy and view operations if the sample is missing
(nor yet created) or the result is different (potentially valid but changed
so that the sample may have to be updated after review).

If the result is missing then the test fails. If the sample is missing then
a warning is written and the sample is created as a copy of the result. The
target directory is also created if it does not exist.

If files are different then the test either fails or, if View is specified
and Fail is not, invokes View, writes a warning, and then prompts to update
the sample file.

File comparison is done via MD5 hashes, it is fast and suitable for large
files. But there is a tiny chance that file differences are not detected.