dpkg-parsechangelog: Rename changelogfile argument to changelog-file

This makes the name consistent with all other instances in the code
base.

debian/changelog

@@ -92,6 +92,7 @@ dpkg (1.18.0) UNRELEASED; urgency=low
     - Clarify dpkg-genchanges changes description open error.
     - Add missing preposition in Dpkg::Source::Patch error message.
     - Improve available state sorting order strings in dselect panel.
+    - Say “changelog-file” instead of “changelogfile” in --help output.
   * Change dpkg-maintscript-helper to handle symlinks and pathnames ending in
     slash. For the former error out, for the latter strip it. Closes: #771752
   * Support moving a conffile not being shipped anymore. Closes: #767003

scripts/changelog/debian.pl

@@ -44,9 +44,9 @@ later for copying conditions. There is NO warranty.
 
 sub usage {
     printf g_(
-"Usage: %s [<option>...] [<changelogfile>]
-
-Options:
+'Usage: %s [<option>...] [<changelog-file>]')
+    . "\n\n" . g_(
+"Options:
       --file <file>       changelog <file> to parse (defaults to '-').
   -l, --label <file>      changelog <file> name to use in error messages.
       --format <output-format>