MFC r270647: Add references to vt(4) and the configuration files in /usr/sha

MFC r270647: Add references to vt(4) and the configuration files in /usr/sha
MFC r270653: Update man-pages to correctly refer to changed pathes and namin
MFC r270657: More man pages that need to know about vt in addition to syscon
MFC r270659: (by pluknet@) Missed comma.
MFC r270660: Back-out the references to vt(4) from this man-page. It appears
MFC r270933: Add references to vt(4) to further man-pages.
MFC r270934: Final patches to the tools used to convert syscons keymaps for
MFC r270935: Add vt(4) support to the console initialisation script, specifi

Second batch of MFCs to add support for Unicode keymaps for use with vt(4).

It contains the following changes:

- Add references to vt(4) to relevant man-pages.
- Update comment in defaults/rc.conf to mention vt
- Update rc.d/syscons to warn about syscons keymaps used under vt.
  An attempt is made to identify the vt keymap to load instead.
- Minor changes to the conversion tool based on mail comments on keymaps.

Relnotes:	yes

git-svn-id: svn://svn.freebsd.org/base/stable/10@271095 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f