Generate an error message when core tries to assign a script's ScriptName which is already assigned.

This means if that happened the core override the older script.
As a result, the earlier one doesn't work and can't deallocate so generates memory leak.

This commit also fixes memory leaks caused by that.

Valgrind log:

==4753== 354 (312 direct, 42 indirect) bytes in 1 blocks are definitely lost in loss record 1,194 of 1,218
==4753==    at 0x4C2626C: operator new(unsigned long) (vg_replace_malloc.c:230)
==4753==    by 0x1039D85: AddSC_go_scripts() (go_scripts.cpp:1015)
==4753==    by 0xDC196F: AddScripts() (ScriptLoader.cpp:534)
==4753==    by 0xC19943: ScriptMgr::ScriptsInit() (ScriptMgr.cpp:70)
==4753==    by 0xD1CCAE: World::SetInitialWorldSettings() (World.cpp:1608)
==4753==    by 0x9100A6: Master::Run() (Master.cpp:234)
==4753==    by 0x90F5D6: main (Main.cpp:146)

--HG--
branch : trunk

0 files changed, 0 insertions, 0 deletions