Implement SASS_PATH

[nottrobin]

This is intended to implement the SASS_PATH environment variable.

Fixes #1678.

Tests

I've added two new API tests under .render:

• "should check SASS_PATH in the specified order"
• "should prefer include path over SASS_PATH"

If you run mocha test/api.js you should see these tests pass.

Manual checking

You can test it manually using the test fixtures as follows:

SASS_PATH is picked up

$ fixdir=`pwd`/test/fixtures/sass-path
$ export SASS_PATH=$fixdir/red
$ bin/node-sass $fixdir/index.scss
body {
  background: red; }

Earlier paths are preferred

$ export SASS_PATH=$fixdir/orange:$fixdir/red
$ bin/node-sass $fixdir/index.scss
body {
  background: orange; }

Specified include-paths still take precedence

$ bin/node-sass $fixdir/index.scss --include-path $fixdir/red
body {
  background: red; }

[nschonni]

This normalization probably belongs up in the getOptions options.includePaths = (options.includePaths || []).join(path.delimiter);, then there is no change anything else

[nottrobin]

I've tidied this up.

[nottrobin]

How can a travis build take quite so long? @nschonni is something up? Is there some way for me to start the travis build again?

[saper]

Looks like OSX jobs got stuck and couldn't even be started.

here's an update from Travis CI https://www.traviscistatus.com/incidents/4mvp857qx8bw

[nottrobin]

Thanks @saper, I hadn't seen that. It's all passed now. @nschonni are you happy that I've address all your points?

[saper]

Looks good to me. Would that be possible to squeeze this into one commit?

[nottrobin]

@saper sure no problem

[xzyfer]

Nice work everyone. Added this to the next.minor milestone. I believe we have one other PR to land in 3.9.0 also.

[nottrobin]

Okay commits squashed into 98c05d4.

[saper]

Big thank you for the contribution!

[nottrobin]

No problem. Thanks for all your help with this @saper et al., it was fun! Do you know when the next minor release will be?