Prepare 3.55 from git

Add git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git submodule

git submodule add \
    git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages-git

Sync to upstream adb7cd33
Update to upstream 18c5047
Update to upstream d6af98f
Update to upstream 82f955d
Update to man-pages-3.55 (move to tarball release later)
Remove man-pages-git submodule and set V to 3.55
Prepare 3.56 from git 6d42f0dc
Sync to git 035bfba7 (3.56 candidate)
Remove man-pages-git submodule and set V to 3.56
Upstream does no more provide .tar.bz2, grab .tar.xz instead
Add fgetc.3 into stdio.cfg and vdso.7 into stdlib.cfg

Add groff_code=verbatim option when processing vdso.7, this
page contains an .if macro.
Sync to man-pages 3.57

Set V=3.57
Workaround formatting issue in ipv6.7
Prepare 3.58-git from fc1d1e69
Update 3.58-git from dec985f9
Update 3.58-git from 90234292
Sync to man-pages 3.58
Sync to man-pages 3.60

Remove special handling of man7 pages, they have been converted
upstream to UTF-8.

Man-pages 3.59 is skipped, two files were wrongly encoded.
Fix po4a -M option, man files have been converted upstream to UTF-8

Remove several -M options, when page is in ascii.
Sync to man-pages 3.61 cadd38ba