ENH: Special highlighting for first (summary) line (length-limited) and following blank line.

Taken from Tim Pope's syntax/gitcommit.vim.
Do not spell-check svn status (added, modified, ...) lines.

Adding the @NoSpell cluster for svnRegion doesn't prevent spell checking for the contained syntax items. Explicitly add @NoSpell there to avoid that the filespecs of added, modified, ... files are spell checked.
Explicitly name contained groups instead using ALL.

The latter is dangerous when another syntax (e.g. via compound filetypes) is added; suddenly all contained groups match in the entire region!
ENH: Introduce different highlight group for the region delimiter.

This: --This line, and those below, will be ignored--
Default to NonText for this (over Comment), as it makes this pure boilerplate less obtrusive.
Update version of svn.vim
Merge the following Ingo Karkat's changes:

ENH: Special highlighting for first (summary) line (length-limited) and
following blank line.

Taken from Tim Pope's syntax/gitcommit.vim.
Remove explicit @Spell groups

It seems explicit @Spell groups disable spell checking for other text in
the message area.