split: take file patterns to limit selection on matching file patterns
When splitting a big changeset, the user often wants to extract specific files
from the changeset while leaving the others files intact.
The split command can now be called with multiple file patterns. Only files
that match one of the patterns will be shown in the interactive selection. The
user will be able to create one or more commits with those files.
When the user finishes splitting the matching files, a last commit will be
made with the remaining of the files.