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

Taken from Tim Pope's syntax/gitcommit.vim.
Merge branches 'svn-NoSpell-status' and 'enh-summary-line'

Conflicts:
	syntax/svn.vim