Throw an error in case of `cd <blah>; <keyword> <path-arg>`

For example, cd foo; use spam.nu * is destined to fail because the cwd is not updated yet when the spam.nu is parsed.

We can fix this for normal command by deferring the path expansion until the eval stage but for keyword commands this cannot work.

We should detect whether cd had been called in the current parse pass and throw an error if we try to call keyword commands with a relative path as an argument.

Start by tracing how cd is handled during a parse pass and how keyword-command arguments reach path expansion and evaluation. Reproduce cd foo; use spam.nu *, then verify that keyword commands with relative path arguments after cd produce an error while normal commands retain their existing behavior.