Whitespace.
Fix a regression introduced by r251967, resulting in:

/usr/libexec/bsdconfig/140.startup/startup: 130:
Syntax error: ";;" unexpected (expecting "fi")
Perform some code consolidation and replace nested case-statements with
more logical if-else statements for each menu selection.
Fix a gcc warning uncovered after r251745.

Reported by:	Sergey V. Dyatko
Reviewed by:	neel
Change the f_dialog_{yesno,noyes}() function-arguments in `dialog.subr' to
accomodate an $hline value for overriding the default. This change does
not effect any current modules as it turns out that not one single usage of
either f_dialog_yesno() or f_dialog_noyes() relied on accepting more than a
first argument (read: all occurrences quoted the first parameter; so $* was
never depended upon).

This will allow some custom invocations of --yesno and --noyes to roll over
to these functions (for example, in `timezone/timezone').
When I first wrote the timezone module, it was in sysutils/tzdialog and it
pre-dates bsdconfig. Update the code to take advantage of f_dialog_msgbox().
Take advantage of newly updated f_dialog_{yesno,noyes}() functions from
SVN r251977 (adding an $hline parameter).
Change a humongous if-statement at the end of f_install_zoneinfo_file() into
an early return, allowing a huge chunk of code to be indented one-level less
Remove extra whitespace lines.