tests: Windows compatibility fixes
- printenv.py, md5sum.py, simplemerge, test-archive, test-merge1,
test-merge-symlinks: set standard streams to binary mode
- test-encode: replace "gunzip" by "gzip -d"
- test-hup: requires fifo
adding a
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
pushing to ../a
abort: could not lock repository ../a: Permission denied