Split PVKII into its own engine branch (#1847)

* Initial PVKII branch support

* Change PVKII code to 23, DOTA uses 22 in MM

* Bunch more SE_PVKII preprocessor that was missed

* Add some missing SOURCE_ENGINE_PVKII cases

* Update PVKII FireOutput signature for Linux

* Update checkout-deps with 'pvkii'

* Fix FireOutput signature for PVKII, accidentally used one from newer build

* Change PVKII code to 10, and bump others by 1

* Only check against SE_SDK2013 here, like Metamod

* More SE_PVKII preprocessor cleanup

loader/loader.cpp

@@ -86,6 +86,7 @@
 #define FILENAME_1_6_CONTAGION		PLATFORM_ARCH_FOLDER "sourcemod.2.contagion" PLATFORM_EXT
 #define FILENAME_1_6_BMS			PLATFORM_ARCH_FOLDER "sourcemod.2.bms" PLATFORM_EXT
 #define FILENAME_1_6_MOCK           PLATFORM_ARCH_FOLDER "sourcemod.2.mock" PLATFORM_EXT
+#define FILENAME_1_6_PVKII			PLATFORM_ARCH_FOLDER "sourcemod.2.pvkii" PLATFORM_EXT
 
 HINSTANCE g_hCore = NULL;
 bool load_attempted = false;
@@ -341,6 +342,11 @@ DLL_EXPORT METAMOD_PLUGIN *CreateInterface_MMS(const MetamodVersionInfo *mvi, co
 			break;
 		}
 #endif
+	case SOURCE_ENGINE_PVKII:
+		{
+			filename = FILENAME_1_6_PVKII;
+			break;
+		}
 	default:
 		{
 			return NULL;