This PR removes some optimistic tests -- a'la "do something,
wait a while, and hope it has trickled through and continue" -- and
instead uses some introspection to ensure that prerequisites are met.
The accountCache contains a file cache, and remembers from
scan to scan what files were present earlier. Thus, whenever
there's a change, the scan phase only bothers processing new
and removed files.
In order to avoid disk thrashing for Accounts and HasAccount,
address->key file mappings are now cached in memory. This makes it no
longer necessary to keep the key address in the file name. The address
of each key is derived from file content instead.
There are minor user-visible changes:
- "geth account list" now reports key file paths alongside the address.
- If multiple keys are present for an address, unlocking by address is
not possible. Users are directed to remove the duplicate files
instead. Unlocking by index is still possible.
- Key files are overwritten written in place when updating the password.