Installation instructions CentOS 6.5

ReadME.MD Adding installation instructions for CentOS 6.5, also adding npm strict-ssl to false to allow some npm packages that have self signed certs.
fixed missing err in upgrade script
#1110 - moved isEmailAvailable into User.email
fixed #1161 properly - Merge remote-tracking branch 'origin/master'

Conflicts:
	src/upgrade.js
removed the postbar selector from activeusers
closes #1167
fixed tests
added back err to redis flushdb
dbmock changes
convert score to int in mongo
added a new property to userData "hasPassword", disabling "current password" field in user editing if no password is set (for SSO logins, for example)
setting password to null in getUserData, because Object.delete is bad? :P (thanks @barisusakli)
Merge branch 'master' of github.com:designcreateplay/NodeBB
Merge branch 'master' of github.com:tparnell8/NodeBB into tparnell8-master
updated readme to point to wiki for platform specific install docs
removing "pluginCSS", "css" in plugins is now included directly into stylesheet.css. This is a breaking change.

fixes #1168
search page change
Merge branch 'master' of https://github.com/designcreateplay/NodeBB
workaround for problem arising from switch to Date.UTC()
Merge branch 'master' of github.com:designcreateplay/NodeBB