Fix error reporting of lessc executable II

[jhnns]

This commit replaces the old control flow of exiting the process when an error occurred which swallowed the error in some situations (#2881). It also adds process.exitCode = 1 in some error situations that have previously been reported as exitCode = 0. Additionally, it adds a listener for "unhandledRejection" to also catch errors caused by rejected promises.

This pull-request incorporates #2882

If you don't want to support node 0.10.x anyway, I can also push a simplified version. Then we probably also should remove the engine property from the package.json.

[matthew-dean]

If you don't want to support node 0.10.x anyway

That seems like a pretty old version to me. In my mind, it's safe to remove 0.10.x support if it simplifies the code.

[matthew-dean]

@less/core Fixing Node 6 support seems like an important PR to get out soon, so can I get some other opinions on this?

[jhnns]

Fixing Node 6 support seems like an important PR to get out soon

This PR is not actually fixing anything for Node 6. As discussed at #2881, the main problem is already fixed on the master branch. Another bug that occurs in combination with the --source-map flag is still present and requires fixing.

This PR fixes the problem that these bugs were even not reported to the user.

[jhnns]

That seems like a pretty old version to me. In my mind, it's safe to remove 0.10.x support if it simplifies the code.

I agree. However, it's still included in the engine field of the package.json. Travis CI is also running node 0.10.x tests.

[matthew-dean]

@jhnns I had a look at Node releases today. The latest 0.10.x release was 4 days ago, same as 0.12. It must be because of their LTS. So I don't think it's safe to remove 0.10.x support. I changed it in the engine field to >=0.12 but we should put support back in for 0.10, and make sure it's passing Travis.

Travis I think still has an outstanding issue where it's not able to install / run PhantomJS sometimes. So you get PR fails when the code is fine, so it's been unfortunately unreliable lately. I tried to tweak settings to get it to work, but it's not my area of expertise.

[jhnns]

I did not remove node 0.10 support. This should work (although I haven't tested it).

Regarding Travis: Have you tried to increase the test timeout?