Add a new function to the cmdline library to determine whether standard input is connected to a terminal device, and set the --non-interactive option if standard input is not connected to a terminal device.
The idea is to make 'svn' non-interactive by default if run from scripts which are launched in some unattended automated fashion. In such a situation it is possible for scripts to hang if 'svn' decides to prompt for information such as login credentials or conflict resolution options.
Also add a new --force-interactive option which enforces the old behaviour.
* subversion/svn/svn.c (svn_cl__longopt_t): Add opt_force_interactive. (sub_main): Set the --non-interactive option based on whether stdin is a tty, unless interactive mode has been forced with --force-interactive. Enforce mutual exclusion of --non-interactive and --force-interactive.