record: add message when starting record's curses interface

We are adding this log message to reduce a confusion when a command prints
something just before starting the curses interface.

Since the interactive mode is taking over the entire screen, starts with no
delay and does wait for a key press, the user believes that messages printed
before opening the interactive mode were actually printed after using
interactive mode, not before.
The fix adds the line "Starting interactive mode" helping the user separate
the messages that were printed before and after the start of the
interactive mode.

One particular example where this was a problem is the revert command where we
first print the list of changes to be considered for revert, then opens the
curses interface right away without letting the user see the messages.
The user then selects the changes, validates and then see the messages from
before opening the interactive mode and is confused.

mercurial/crecord.py

@@ -477,6 +477,7 b' def chunkselector(ui, headerlist):'
     of the chosen chunks.
 
     """
+    ui.write(_('starting interactive selection\n'))
     chunkselector = curseschunkselector(headerlist, ui)
     curses.wrapper(chunkselector.main)