[trac2367_v2] sort help string components and fix one name

sorted the individual components in the help string

and changed dns_libraries to dnslibs
[trac2367_v2] fix spelling typo in help message
[2367_v2] Shorten help message to most common options

Rather than display the list of all components, which may lead users
to expect they can configure and build just a single component, adjust
the help string for --enable-components to just list the meta-names for
DNS, DHCP and common code. All of the other component names still
exist, so fine-grained control is still possible, but that is not the
intent behind this option.