provide WithCloseOnExec varients of rest of file opening functions

[joeyh]

#21 added openFileWithCloseOnExec and openExistingFileWithCloseOnExec to the Internal module, but the following other functions in file-io do not support setting the close on exec flag at open time:

openBinaryFile
withFile
withBinaryFile
readFile
writeFile
appendFile
openTempFile
openBinaryTempFile

I could use every single one of these if they existed, since I want to avoid all possible file descriptor leaks in my program.

I do understand that file-io is only aiming to replicate base behavior, and so it may seem that you have embarked on a slippery slope with #21. If you feel that is the case, maybe it would make sense to have a file-io-closeonexec? In that case, it would make sense to at least provide something in the file-io Internal module that can be used to make an openTempFile that sets CloseOnExec, to avoid quite a lot of complicated code duplication. The rest can be implemented easily enough externally to file-io using withOpenFile'.