Set proper diffing for sqlite database

To get proper diffs from sqlite we need:

in .gitattributes or .git/info/attributes a line like:

gatoscript.db diff=sqlite3

in .git/config or $HOME/.gitconfig two lines like:

[diff "sqlite3"]
    textconv = dumpsqlite3

and last, somewhere in our path a "dumpsqlite3" script like:

#!/bin/sh
sqlite3 $1 .dump
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