eblob: completely removed compression support
blob: fixed read with offset/size set

Reported by: elessar@
XXX: blob: use new writev()-like libeblob APIs

This greatly simplifies backend code by moving all work behind eblob's
BLOB_DISK_CTL_EXTHDR flag.
blob: use eblob_read_return() instead of eblob_read_nocsum()
blob: fixed formatting
blob: added shortcut 'b' to 'c->eblob'
leveldb: fixed write of timestamp/user_flags
leveldb: removed leveldb backend

Requested by: zbr@
recovery: python 2.6 compat