Update assetgraph to 1.5.12.
Use setImmediate instead of process.nextTick if available.

(cherry picked from commit c73e0c1ca65fdb99ca587869f1ec18835688fea9)

Conflicts:
	test/buildProduction-test.js
Replace memoizer with memoizesync.

(cherry picked from commit 1e3700e8f8a237066e78b0d19e9b82fcc2f4c419)

Conflicts:
	lib/i18nTools.js
1.7.15