Function: vc-next-action

Do the next logical version control operation on the current fileset.
This requires that all files in the current VC fileset be in the
same state. If not, signal an error.

For merging-based version control systems:
If every file in the VC fileset is not registered for version
control, register the fileset (but don't commit).
If every work file in the VC fileset is added or changed, pop
up a *vc-log* buffer to commit the fileset.
For a centralized version control system, if any work file in
the VC fileset is out of date, offer to update the fileset.

For old-style locking-based version control systems, like RCS:
If every file is not registered, register the file(s).
If every file is registered and unlocked, check out (lock)
the file(s) for editing.
If every file is locked by you and has changes, pop up a
*vc-log* buffer to check in the changes. If the variable
`vc-keep-workfiles' is non-nil (the default), leave a
read-only copy of each changed file after checking in.
If every file is locked by you and unchanged, unlock them.
If every file is locked by someone else, offer to steal the lock. (fn VERBOSE)