Allow backslash ('\') and at ('@') characters in USERNAME grok pattern

[kanarip]

Allow backslash ('') and at ('@') characters as part of the auth field in standard combined Apache httpd log entries (field #3).

Necessary in order to be able to parse the log entries provided as samples / tests.

[elasticsearch-release]

Can one of the admins verify this patch?

[jordansissel]

For Logstash 1.5.0, we've moved all plugins (and grok patterns) to individual repositories. Can you move this pull request to https://github.com/logstash-plugins/logstash-patterns-core?

This sequence of steps may help you do this migration:

1. Fork this repository

2. Clone your fork

   git clone https://github.com/kanarip/logstash.git

3. Create a branch:

   git checkout -b my-branch-name

4. Apply the patches from this PR into your branch:

   curl -s https://github.com/elastic/logstash/pull/1224.patch | git am

   This should take your commits from this PR and commit them to your new local branch.

5. Push!

   git push origin my-branch-name

6. Open a new PR against https://github.com/logstash-plugins/logstash-patterns-core

7. Sign the CLA

   Our CLA check indicates that some commit authors have not signed the CLA or are not members of Elasticsearch. See our contributor agreement for more details. :)