improve diagnostics in case of common startup issues

[tjanczuk]

http://encosia.com/resolving-an-iisnode-the-service-is-unavailable-503-error/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+Encosia+%28Encosia%29

[tjanczuk]

Fixed in f1fd9f1

A new configuration setting iisnode/@devErrorsEnabled was added. Default is true. When the setting is true, for the most common error conditions iisnode will return an HTTP 200 response with [lightweight] HTML body explaining the issue and possible ways of fixing it. If @devErrorsEnabled is false (recommended in production), iisnode will return a generic HTTP 5xx response.

Some of the most common issues for which iisnode will return a verbose HTTP 200 response are:

1. Lack of necessary permissions to create a log file to redirect stdout and stderr from a node.exe process.
2. Cannot file node.exe in the configured location
3. Lack of necessary permissions to deploy supporting files necessary to initialize a debugging session.