add support of @ to column names

[githubmanticore]

currently where is no way to create index with @timestamp column when use that via HTTP interface for filtering or at aggs. It could be better to add support of this and make that to not conflict with @uservars

[githubmanticore]

➤ Stan commented:

fixed at 651e158 and 052c7c1

added @ symbol to be a part of the column name; rolled back @ replacement; fixed error reply for failed _search requests; fixed reply for set global es_compat; fixed document id from the logstash; added regressions to test 458