Fixed a bug that RecordFilterMixin does not work with stream with multiple records

"format_stream" passes tag variable to "filter_record" without deep
copying.
It works fine when there is only 1 record in stream.
But If the stream have n records, filter_record filters tag n times.
fix to show error class name in log
Fixed code formatting issues

- add space between , and tag
- use dup to clone string object
Merge pull request #109 from tomohisaota/fix-mixin

Fixed a bug that RecordFilterMixin does not work with stream
fix to ignore error in signal trap context, fails to get thread lock to Engine.emit
fix not to call Fluent::Engine.stop 2 or more times, for process group killed situation on foreground
fix to mark shutting down situation before actual shutdown
Merge pull request #128 from tagomoris/log_error_classname

fix to show error class name in log
Stop using a cached unpacker for MessagePackEventStream.

Sharing a a single instance of MesspaPack::Unpacker between input plugins and
MessagePackEventStream instances is unsafe. A test case has been added
to prove how easy it is leak events with the copy plugin and multiple
output plugins.
Merge pull request #132 from tagomoris/ignore_log_emit_in_trap_thread

fix to ignore error in signal trap context
Merge pull request #137 from abecciu/copy-plugin-event-leak-fix

Fix copy plugin event leak and fix undefined Test::Unit::AssertionFailedError bug in ruby trunk.
Add msgpack 0.4.x test to out_copy
add command line option to suppress error logs with specified interval (to avoid fluentd error log storm)
Merge pull request #134 from tagomoris/suppress_exec_filter_log

add option to suppress error logs with specified interval
Merge pull request #133 from tagomoris/signal_handle_for_foreground

Signal handle for foreground
Check MessagePack version to prevent MessagePack 4 performance degression
Remove unneeded require
v0.10.34
Update FailureDetector class of out_forward.rb

The method 'phi(now) of 'FailureDetector class calculates the variable 't wrong way.

When @heartbeat_interval is not the default value (1 sec), 't value contains @heartbeat_interval time. But 'mean doesn't. So @heartbeat_interval is set higher, 'phi(now) returns a higher value.
fix unix domain socket connection leak.

fixed review.

change error message.