"Cannot find module" message should be more explicit, saying where it's looking

With all the vagaries around module loading, it'd be great to give a more verbose, helpful error message for "Cannot find module 'foo'", saying where the compiler looked for the module. That can help clue the user into (1) how TypeScript works and (2) how to fix their issue.

The message text could be semi-static, maybe something like: IF using commonjs loading AND path isn't relative THEN say "Couldn't find module Foo; searched node_modules directory off directory XXXX and its ancestors and the package.json Typings path YYYY.

Better doc around the module loading algorithm helps, but just putting some of that info in the error message makes it very easily discovered. It also helps clue the user into what isn't the problem (e.g. the message above confirms that using commonjs module loading & found Typings in package.json, but something else seems to be the problem).

首先阅读 issue 中关于 CommonJS 模块加载、祖先目录中的 node_modules 搜索以及 package.json 中 Typings 路径的描述。跟踪编译器的模块解析和诊断入口点，然后找出现有的 "Cannot find module" 错误测试。完成的标准是：诊断信息说明了解析搜索过的位置，同时不掩盖原始失败原因。