Fix some issues reported by lintian

Fix some issues reported by lintian

• Update watch file format version to 4. (older-debian-watch-file-standard)
• Bump debhelper from old 12 to 13. (package-uses-old-debhelper-compat-version)
• Set debhelper-compat version in Build-Depends. (uses-debhelper-compat-file)
• Update standards version to 4.4.1, no changes needed. (out-of-date-standards-version)

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in second set of .debs but not in first

-rw-r--r--  root/root   /usr/lib/debug/.build-id/60/e5d45fe6df697fa0c2d532343b3257d5e0a127.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/64/e188e61bc037fef2fbe7f5c22889d8cacbbbf1.debug

No differences were encountered between the control files of package **ahcpd**

Control files of package ahcpd-dbgsym: lines which differ (wdiff format)

• Build-Ids: 64e188e61bc037fef2fbe7f5c22889d8cacbbbf1 60e5d45fe6df697fa0c2d532343b3257d5e0a127

You can also view the diffoscope diff (unfiltered).

This merge proposal was created by the Janitor bot, and it will automatically rebase or close this proposal as appropriate when the target branch changes. Any comments you leave here will be read by the Janitor's maintainers.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/ahcpd/f3958030-64fc-41d7-a60f-d3c0b3a8dcc9.