rollback file itself in emergency if could.

explicitly use "return".
modify error messages.
ensure initialized value.

o not apply quotemeta() for key.
o autoflush(1)
o check the number of matching, return error if no any matched line.

sequence_increment verifies if the value is writtern.

+ sequence_increment()
+ sequence_replace()

provides lock() and unlock() metohds though file map only is
supported.

FML::Process::Kernel is switched to IO::Adapter based lock.

o fix comments.
o fix loop label name.
o more correct initialization if could.
o use //o;