Allow selection to be overriden by $SELECTION

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Suggested-by: nand <nand@nand.wakku.to>
Keepass import should include root-level entries

Repro steps:
1. In KeePass, add some entries as children of the root node
2. Export the KeePass to foo.xml
3. 'keepass2pass.py -f foo.xml'
Expect: all entries imported
Actual: root-level entries are skipped
Makefile: appropriate mkdir -p for completion

Fix for c832d4647439a0d504a310fba51f20dcb5051c47