Make Module::Refresh a core dependency

This means that --devel-mode is only necessary for people who intend to
run tests or do other development of RT, but that users who merely
intend to extend RT using Mason, for instance, do not need the extensive
list of dependencies used during testing.
Rename --devel-mode to --developer, to make break in meaning clear

Previously, --devel-mode both added the dependencies needed for testing
RT, as well as setting the default value of $DevelMode in RT_Config.pm
These actions are orthogonal, as many users wish to enable $DevelMode
but do not need the additional dependencies; and developers may not wish
to run with $DevelMode.

By renaming the option, existing users of --devel-mode will no longer
have the additional dependencies if all they wish is Module::Refresh.
This also makes the setting of $DevelMode in RT_Config.pm no longer
controlled at configure-time, which is an odd action-at-a-distance, as
it means one RT's defaults are malleable from one install to another.
Consistency is improved by forcing users to add it to RT_SiteConfig.pm,
like any other option.
Sort dependencies and remove duplicates
Merge core dependencies into one list, and eliminate duplicates

PSGI and MASON are core dependencies which cannot be disabled using
command-line flags; fold them into CORE.  Though CLI and MAILGATE are
similarly required, and cannot be disabled using command-line flags,
keep them separate for now, as they are standalone binaries which are
intended to be able to be distributed separately.  Keeping a separate
list of their dependencies is thus of use.
Rename --with-postgresql to --with-pg, which is what the makefile calls
Minor reformatting of options and POD
Merge branch '4.2/devel-mode-and-testdeps'