grep: fix hash(linestate) to not include linenum
linestate.__eq__() just compares the line values whereas __hash__() does
hash both self.line and self.linenum, which violates the rule. __hash__()
was added at
fb502719c75c, "python 2.6 compatibility: add __hash__ to
classes that have __eq__" with no additional remarks, so this would probably
be a simple mistake.
The test output changed because difflib.SequenceMatcher() internally uses
a dict. As you can see, the line "export" is unchanged at the revision 2,
so the new output is correct.
test-grep: document that trivially moved lines might not be detected
I'm not going to fix this. I just learned "grep --diff" does clever thing
than a simple grep(patch.diff(context=0)), and I think it's better to
document how things work.