Fixes https://github.com/tendermint/tendermint/issues/1189
For every TxEventBuffer.Flush() invoking, we were invoking
a:
b.events = make([]EventDataTx, 0, b.capacity)
whose intention is to innocently clear the events slice but
maintain the underlying capacity.
However, unfortunately this is memory and garbage collection intensive
which is linear in the number of events added. If an attack had access
to our code somehow, invoking .Flush() in tight loops would be a sure
way to cause huge GC pressure, and say if they added about 1e9
events maliciously, every Flush() would take at least 3.2seconds
which is enough to now control our application.
The new using of the capacity preserving slice clearing idiom
takes a constant time regardless of the number of elements with zero
allocations so we are killing many birds with one stone i.e
b.events = b.events[:0]
For benchmarking results, please see
https://gist.github.com/odeke-em/532c14ab67d71c9c0b95518a7a526058
for a reference on how things can get out of hand easily.
if we call it after, we might receive a "fresh" transaction from
`broadcast_tx_sync` before old transactions (which were not
committed).
Refs #1091
```
Commit is called with a lock on the mempool, meaning no calls to CheckTx
can start. However, since CheckTx is called async in the mempool
connection, some CheckTx might have already "sailed", when the lock is
released in the mempool and Commit proceeds.
Then, that spurious CheckTx has not yet "begun" in the ABCI app (stuck
in transport?). Instead, ABCI app manages to start to process the
Commit. Next, the spurious, "sailed" CheckTx happens in the wrong place.
```
* Vulnerability in light client proxy
When calling GetCertifiedCommit the light client proxy would call
Certify and even on error return the Commit as if it had been correctly
certified.
Now it returns the error correctly and returns an empty Commit on error.
* Improve names for clarity
The lite package now contains StaticCertifier, DynamicCertifier and
InqueringCertifier. This also changes the method receivers from one
letter to two letter names, which will make future refactoring easier
and follows the coding standards.
* Fix test failures
* Rename files
* remove dead code
