Added logic to enforce rule that RHS of a String option cannot
be blank.
Undid forced case collapse of Win32 file names.  Instead, now
under Win32, both directory and file names are sorted using
a case-insensitive algorithm.
Factored menu update logic into a single, common handler
which can talk to either standard functions or event
handlers (via the 'fakeevent' option).
Both MAXDIR and MAXHIST are now observed on a config file reload.
However, they do not actually remove content from their respective
data structures.  They merely limit what is visible.  This allows
a subsequent change to restore the view of previous entries.