[$] From O_MAYEXEC to trusted_for()

The ability to execute the contents of a file is controlled by theexecute-permission bits - some of the time. If a given file contains codethat can be executed by an interpreter - such as shell commands or code in alanguage like Perl or Python, for example - there are easy ways to run the interpreter onthe file regardless of whether it has execute permission enabled or not.Mickael Salaun has been working on tightening up the administrator'scontrol over execution by interpreters for some time, but has struggled tofind an acceptable home for this feature. His latest attempt takes theform of a new system call named trusted_for().