cherry-pick from master

- Update to 2.7.3 due a vulnerability that affect all versions 2.x. [1]
- Update MASTER_SITES.
- Convert to optionsNG.
- Trim header.

More info:
https://github.com/SpiderLabs/ModSecurity/blob/master/CHANGES

Reported by:    olli hauer <ohauer@gmx.de> [1]
Approved by:    portmgr (bdrewery)
Security:       2070c79a-8e1e-11e2-b34d-000c2957946c

Conflicts:
	security/vuxml/vuln.xml