tests/test-custom-filters.out

test-merge-tools: windows fixes

- /bin/cat does not exist, expect 'cat'
- non-interactive mode is not correctly detected in pysh, force it

% Repository data:
Some stuff to ponder very carefully.
% Fresh checkout:
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Copyright 2046, The Masters
Some stuff to ponder very carefully.
M stuff.txt
% Problem encoding:
abort: missing header "Copyright 2046, The Masters" in morestuff.txt
M stuff.txt
A morestuff.txt