Code can now call begin_reversible_command and commit_reversible_command around a region
of code which itself calls those functions (and so on), areas contained within enclosing
regions will be added as sub-commands of the current command (i.e. it's a stack).
Fixes mantix issue #0002558.
git-svn-id: svn://localhost/ardour2/branches/3.0@5051 d708f5d6-7413-0410-9779-e7cbd77b26cf
David Robillard
83c27fa888