convert all readFile, writeFile, and appendFile to close-on-exec safe versions

convert all readFile, writeFile, and appendFile to close-on-exec safe versions

Even in the Build system. This allows grepping to make sure that there
are none left un-converted:

git grep "writeFile" |grep -v F\\.| grep -v doc/|grep -v writeFileString | grep -v writeFileProtected |grep -v Utility/FileIO
git grep "readFile" |grep -v F\\.| grep -v doc/|grep -v readFileString |grep -v Utility/FileIO
git grep "appendFile" |grep -v F\\.| grep -v doc/|grep -v appendFileString |grep -v Utility/FileIO

Might be nice to automate that to prevent future mistakes...

Sponsored-by: the NIH-funded NICEMAN (ReproNim TR&D3) project