"extends" field is not respected

When ctsc is running custom tsconfig that extends from other tsconfig, it doesn't follow the extends field.

Below is an example to reproduce the problem.

**tsconfig.build.json**:
```typescript
{
"extends": "./tsconfig.json",
"exclude": [
"node_modules",
"test",
"dist",
"**/*spec.ts",
"scripts",
"www"
]
}
```

**tsconfig.json**
```typescript
{
"compilerOptions": {
"module": "commonjs",
"sourceMap": true,
"outDir": "./dist",
"baseUrl": "./"
},
"exclude": [
"node_modules",
"dist",
"scripts",
"www"
],
"include": [
"src"
]
}
```

When the command `ctsc -p tsconfig.build.json` is ran, it complaints for `No include found in tsconfig /path/to/tsconfig.build.json`. This error is unexpected, because the "include" field could be read from the extended file "tsconfig.json" in the example.