xgettext improvements for Guile and Scheme

[Bruno Haible]

Hi,

The next GNU gettext release will have the following improvements for
Guile and Scheme source files:

* Programming languages support:
  - Scheme:
    o xgettext now supports the option '-L Guile' as an alternative to
      '-L Scheme'.  They are nearly equivalent.  They differ in the
      interpretation of escape sequences in string literals: While
      'xgettext -L Scheme' assumes the R6RS and R7RS syntax of string literals,
      'xgettext -L Guile' assumes the syntax of string literals understood by
      Guile 2.x and 3.0 (without command-line option '--r6rs' or '--r7rs', and
      before a '#!r6rs' directive is seen).
    o xgettext now recognizes comments of the form '#; <expression>'.

If you want to review how it works, feel free to use a snapshot tarball,
such as from <https://gitlab.com/gnu-gettext/ci-distcheck> .

Bruno