rebase-i: explicitly accept tab as separator in commands

rebase-i: explicitly accept tab as separator in commands

The git-rebase-todo is parsed several times with different parsers. In
principle, the user input is normalized by transform_todo_ids and
further parsing can be stricter.

In case the user wrote

pick deadbeef<TAB>commit message

the parser of transform_todo_ids was considering the sha1 to be
"deadbeef<TAB>commit", and was leaving the tab in the transformed sheet.
In practice, this went unnoticed since the actual command interpretation
was done later in do_next which did accept the tab as a separator.

Make it explicit in the code of transform_todo_ids that tabs are
accepted. This way, code that mimicks it will also accept tabs as
separator.

A similar construct appears in skip_unnecessary_picks, but this one
comes after transform_todo_ids, hence reads the normalized format, so it
needs not be changed.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>