tests: no need to explicitly export HOME in test files
the test runner ensures that HOME is set to a temp dir
tests: set HOME to the test temp dir (
issue2707)
dirstate: eliminate _lastnormal set
We can get rid of the _lastnormal set by using the filesystem mtimes to
identify the problematic "lastnormal" files on status(), forcing a file
content-comparison if the file's mtime timeslot is equal to _lastnormaltime.