plugins/resman: Offest 0x10 of CResStruct is a CKeyTableEntry not a pointer to a resref.

* Add CKeyTableEntry struct from API
* Remove saveName member from CNWNXResMan, it's not needed and only leaks the string
  previous placed into offset 0x10 of CResStruct
plugins/resman: Replace GNU ext/hash_map with std::unordered_map

* Add -std=c++0x to C++ compile flags.
plugins/resman: Initialize size member of ResManDemandStruct with 0 instead of NULL to get rid of warning.
plugins/resman: Use stat struct types in CResFileInfo to get rid of unsigned/signed comparison error.
plugins/resman: Fix CResNCS memory leak.

The engine doesn't deallocate CResNCS, unless in an out of memory scenario.

* Add data member to CResFileInfo and default constructor to cache NCS resources.
* Change hash table key to resref + extension, to unify file and event hook sources.
* Refactor a bit to avoid code duplication.
plugins/resman: Expand events to communicate better with consumers.

* Add resource exists event hook.
* Expand demand resource hook to communicate time.