Refactor: consolidate the PlatformContext-related externs.

Move their declarations out of cf3.*.h, to a header file of their own,
and move an associated definition from cf3globals.c to classes.c so
that they're all in one place.  Renamed classes.c to systype.c and
named the header systype.h, since this name more faithfully relates to
the actual function of PlatformContext (it says what type of system
we're running on).  Adjust includes and make-files to match.
Spacing changes.

Line up assorted comments tidily, purge dangling hspace, put space
round some operators, kill a blank line.
redmine3974: add "Sun solaris" platform type.

This distinguishes solaris with BSD-style tools in /usr/ucb/ from more
modern versions where the system tools are BSD-compatible.  For now,
there is no difference; this is preparation for adding differences.
Documented what various platforms are a bit more clearly.

Note on the name: although Oracle took over before SunOS 5.10 was out,
the versions with /usr/ucb/ were part of the Sun era; and we need a
simple variant on the name to distinguish the two cases.  Using prefix
OLD has the perennial problem that, some day, what's currently new
shall be old.  It seems unlikely that Sun shall ever be an independent
entity again, so using its name looks like a better choice.
solaris: extend ps command column width and prepend zone name
Merge pull request #1794 from MatthewCattell/prepend-solaris-zone-extend-cmd-len

Prepend solaris zone extend cmd len