* Use `subtle::slices_equal` for constant time comparison.
Also update the existing version of subtle in `ethcrypto` from
0.1 to 0.5
* Test specifically for InvalidPassword error.
This is a huge change, which includes some changes to replace code that
originally cloned to reuse allocations instead. The updated
`elastic-array` crate renames its consuming `Vec`-conversion method to
`into_vec`, which means that I can do a simple
`sed -i 's/to_vec/into_vec/'` and then fix the compilation errors.
This commit is probably a minor performance win and definitely a
significant readability win.
* easy to use conversion from and to string for ethstore::Crypto
* ethstore uses tempdir instead of devtools
* ethstore does not depend on ethcore-util
