The .gitattributes cache should not reload .gitattributes in the
middle of checking out, only between checkout operations. Otherwise,
we'll spend all our time stat'ing and read'ing the gitattributes.
Created a copy of tests/resources/testrepo.git that is compatible
with the Clar sandboxing helpers.
Restructured commit test suites to use Clar sandbox helpers.
Now using typed data arrays rather than lots of macros to define test
cases.
