fixup! SConstruct : Ensure gaffer wrapper exists before calling `us…

…dGenSchema`

SConstruct

@@ -1780,7 +1780,6 @@ for libraryName, libraryDef in libraries.items() :
 		if additionalFile in pythonFiles :
 			continue
 		additionalFileInstall = env.InstallAs( os.path.join( installRoot, additionalFile ), additionalFile )
-		env.Alias( "additionalFiles", additionalFileInstall )
 		env.Alias( "buildCore", additionalFileInstall )
 
 	# osl headers
@@ -1860,14 +1859,14 @@ for libraryName, libraryDef in libraries.items() :
 		# Then call `usdGenSchema` to write `generatedSchema.usda` and
 		# update `plugInfo.json` in place.
 
+		schemaCommandEnv = commandEnv.Clone()
+		schemaCommandEnv["ENV"]["PYTHONPATH"] += os.path.pathsep + schemaCommandEnv.subst( "$BUILD_DIR/python" )
 		subprocess.check_call(
 			[
-				shutil.which( "gaffer.cmd" if sys.platform == "win32" else "gaffer", path = env["ENV"]["PATH"] ),
-				"env",
-				"usdGenSchema.cmd" if sys.platform == "win32" else "usdGenSchema",
+				shutil.which( "usdGenSchema.cmd" if sys.platform == "win32" else "usdGenSchema", path = schemaCommandEnv["ENV"]["PATH"] ),
 				str( source[0] ), targetDir
 			],
-			env = env["ENV"]
+			env = schemaCommandEnv["ENV"]
 		)
 
 	schemaSource = os.path.join( "usdSchemas", libraryName + ".usda" )
@@ -1880,7 +1879,6 @@ for libraryName, libraryDef in libraries.items() :
 			schemaSource,
 			buildSchema
 		)
-		env.Depends( generatedSchema, "additionalFiles" )
 		commandEnv.Alias( "buildCore", generatedSchema )
 
 env.Alias( "build", "buildCore" )