Python-application

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* Added workaround for logging unicode and string objects
* Don't apply str over log records diverted from Twisted
* Fixed the wrapper's default arguments when preserving function signatures

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* Fixed cleaning up observer weakref proxies after recent Singleton changes
* Return False instead of 0 from NullType.__nonzero__
* Made Null only compare equal with itself
* Removed obsolete application.python.util module

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* Renamed Singleton's internal attribute to make them less obtrusive
* Fixed detection for the class's __new__ in Singleton
* Added execute_once decorator

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* Reorganized the application.python package contents
* Added the limit function to restrict a numeric value to a given range
* Added function to recursively create directory and ignore error if exists
* Added classproperty descriptor for defining properties at the class level
* Removed obsolete default_host_ip attribute from application.system
* Improved Null to better act as a class substitute

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* Release EventQueue events immediately after processing

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* Use the system path separator when building the list of packages
* Fixed handling of unicode in the syslog logger