check whether accounts and snapshots are using the same path

[yihau]

Problem

both accounts and snapshots have the same name subdirectory, snapshot. catch this situation earlier to prevent unexpected behavior.

Summary of Changes

• ensure account_path and snapshot_path are unique
• add test for it

[brooksprumo]

"Hilariously", the "snapshots" subdirectory is not standard...

--snapshots will create a "snapshots" subdirectory
--accounts will create a "snapshot" subdirectory

note the missing S above!

But, when using ledger tool, the subdirectory for snapshots under the ledger path will be "snapshot" (no S)!

I think we'll want to fixup the ledger-tool stuff. And all of this pain caused by using string literals instead of constants...

I do think enforcing unique-ness here is a good idea. The snapshot-vs-snapshots is confusing, and could cause issues when running ledger-tool.

[steviez]

I think we'll want to fixup the ledger-tool stuff. And all of this pain caused by using string literals instead of constants...

Yeah, I'm down for making ledger-tool consistent with validator.

Also, I think we should potentially expand further and check for uniqueness of other specifiable paths. A few weeks ago, I hit an issue because I accidentally specified several items to be at the same path (--ledger) instead of specifying unique sub-directories for each.

[brooksprumo]

The changes look good to me, thanks! Some tiny nits/requests:

[brooksprumo]