bug#28295: better error messages: missing closing parenthesis

[Ricardo Wurmus]

A person who does not use paredit can easily create a source file that
does not have matching parentheses.  Loading a broken file currently
produces an error like this:

--8<---------------cut here---------------start------------->8---
$ guile -e '(hello'
ERROR: In procedure read:
ERROR: In procedure scm_i_lreadparen: #<unknown port>:1:7: end of file
--8<---------------cut here---------------end--------------->8---

For new users it is not obvious that this error message means that a
closing parenthesis is missing.

Can the message be improved?

--
Ricardo

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