manages the @::str array and associated strings.txt files

Usage:

lang.pl show
lang.pl switch num1 num2
lang.pl audit

[show]
Scans all codes files in 'dir' and displays how many times each
str[] is used.  Will print warnings for strings that aren't
used, or strings that are referenced as a range.

[switch]
Replaces the positions of str[] "num1" and "num2" in all
the code files and in the English strings.txt file.  This is
used to move holes in strings.txt to the end where they can
be safely stripped, and to move public strings to the top of
the file so that the public process can abort reading of
strings.txt early on.

Warning: bands 21-40 and 121-200 are reserved for Common.pm
modules which are shared across multiple scripts.  Do not switch
strings into or out of those bands.

[audit]
Checks non-English language strings to confirm that $s1/$s2
sequences are preserved.