Avoid variable expansion and stripping leading spaces in 'read_line'

On Windows, `read_line`
- can't handle a leading `=` character (it crashes)
- strips any leading spaces from the input
- expands any variables (e.g. if the user enters `%path%`, the stored result is the value of the user's `path` environment variable rather than the string `%path%`).

This patch fixes these issues.