Add case insensitive option to file directory/exist functions


in the docs, to handle case, sometimes we need to check the case of the path and get it exact,
now i know this can be addressed in other ways, but it would be nice to have a BIF option
to match case.

an automatic case insensitive match would save a lot of pain for cross platform code on case (in)sensitive file systems, i.e windows vs unix file systems

something like (dunno about returnMatch, but you know what i mean)

// returns either the exact case filename or an empty string
FileExists(source=filePath, returnMatch=true);

// returns either exact case directory or an empty string
DirectoryExists(source=filePath, returnMatch=true);