Deal with abs_path change in new version of perl, now it returns undefined when the directory does not exist.

This may cause other breakage; I only fixed the case I was seeing, where
a ~/.mrtrust that referred to a directory that does not exist failed.
prep
Always print a new line after failed commands.
Pass a fake terminal to subcommands when mr is run in a terminal.

This is needed so that programs that print color to terminals
but not to pipes continue to do so when mr redirects output
to a variable before printing it or not printing it.
Add a minimal output mode that shows output when appropriate. Closes: #694031
changelog
fix uninitialized value
fix