Issues: SEC-2098, SEC-2099

AddHeadersFilter for setting security headers added including a bean definition parser for easy configuration of the headers. Enables easy configuration for the X-Frame-Options, X-XSS-Protection and X-Content-Type-Options headers. Also allows for additional headers to be added.
Merge remote-tracking branch 'origin/add-headers' into add-headers

Conflicts:
	config/src/main/resources/org/springframework/security/config/spring-security-3.2.rnc
	config/src/main/resources/org/springframework/security/config/spring-security-3.2.xsd
	web/src/main/java/org/springframework/security/web/headers/AddHeadersFilter.java