If the quotes.txt file doesn't exist with the right case, try any case

(but prefer the proper/configured case, based on config in SCFG).

Works around a problem where DDMsgReader always creates QUOTES.TXT (never
quotes.txt), but SBBS tries to read in the file with the case it expects.
This wouldn't be a problem on case-insensitive file systems (Windows).

Resolves the writemsg.cpp error reported by Nelgin