blob: moved mutex init to separate function
stats: improved stats naming
hash: simplify hash entry add

Since types were removed we can't have entries with different sizes in
one hash.
hash: reduce memory consumption by 10%

Since columns removal we have only fixed sized entries in hash so we
should not store size of each cached value.

New eblob_hash_entry size is 88 bytes against 96 of old one (on x86_64).
hash: check rwlock_init return code
hash: keep track of replaced entries
stats: accounting for in-memory index size
stats: simplified stats naming

Renamed `index_corrupted_entries` to `records_corrupted`.