Acivate specs for issue 550

Needed to fix another spec test (ruby sass still passes).
The specific issue has been extracted to its own spec test.
https://github.com/sass/libsass/issues/623
Merge pull request #129 from mgreter/issue/activate/550

Acivate specs for issue 550
Add specs for nth with maps
Merge pull request #134 from xzyfer/wip/issue-643

Add specs for nth with maps
issue 641 test case
Merge pull request #135 from matthewlein/issue_641

Add spec for issue 641
Add specs for issue 639
Add specs for issue 644
Add specs for issue 590
Merge pull request #137 from xzyfer/feat/specs-171114

Add missing for Libsass issues as of 17/11/14
Activate specs for issue 534
Merge pull request #138 from xzyfer/wip/activate-issue-534

Activate specs for issue 534
Activate specs for issue 641
Merge pull request #139 from xzyfer/wip/activate-issue-641

Activate specs for issue 641
Activate specs for issue 368
Merge pull request #140 from xzyfer/wip/activate-issue-368

Activate specs for issue 368
add test that checks not expressions in declaration are not evaluated

see https://github.com/sass/libsass/pull/349
Merge pull request #95 from nsams/not-expr-in-declaration

add test that checks not expressions in declaration are not evaluated
Revert "Activate specs for issue 368"
Merge pull request #141 from sass/revert-140-wip/activate-issue-368

Revert "Activate specs for issue 368"