Remove trailing whitespace.

`sed 's/[[:space:]]*$//'`
Replace tabs with spaces.

`sed 's/\t/    /g'`
Line up indentations properly.

`sed -E 's/^((    )*) {1,3}([^ ])/\1\3/'`
(Thanks to @warpr and @JonnyJD for help with cracking that one!)
Manual indentation of $.ajax() call in discogs_importer.user.js.

Follow-up to commit 1a3a2414dc.