(exec_extension_view): refactoring: remove temporary file in exec_extension().

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(regex_command_for): new function to use regex_command in already created viewer/editor

...and related changes.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Fix mode switch after CK_FileNext/CK_FilePrev.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>