Have npm run typings use built directory; fix typescript tests

* Modify scripts/gulpfiles/typings.js to write typings to BUILD_DIR.
* Modify tests/scripts/compile_typings.sh to check compilability of
  resulting output from BUILD_DIR.
* Rename checkin script to checkin:built, add a checkin:typings script
  to do the same for .d.ts files, and a new checkin script to do both.
* Have recompile run checkin:typings.

gulpfile.js

@@ -32,10 +32,9 @@ module.exports = {
   buildCompressed: buildTasks.compressed,
   buildGenerators: buildTasks.generators,
   buildAdvancedCompilationTest: buildTasks.advancedCompilationTest,
+  checkin: gulp.series(buildTasks.checkinBuilt, typings.checkinTypings),
   checkinBuilt: buildTasks.checkinBuilt,
-  clean: gulp.series(
-      buildTasks.cleanBuildDir,
-      packageTasks.cleanReleaseDir),
+  clean: gulp.series(buildTasks.cleanBuildDir, packageTasks.cleanReleaseDir),
   cleanBuildDir: buildTasks.cleanBuildDir,
   cleanReleaseDir: packageTasks.cleanReleaseDir,
   gitSyncDevelop: gitTasks.syncDevelop,
@@ -43,6 +42,7 @@ module.exports = {
   gitCreateRC: gitTasks.createRC,
   gitUpdateGithubPages: gitTasks.updateGithubPages,
   typings: gulp.series(typings.typings, typings.msgTypings),
+  checkinTypings: typings.checkinTypings,
   package: packageTasks.package,
   checkLicenses: licenseTasks.checkLicenses,
   recompile: releaseTasks.recompile,