Update libsass to latest (local) version
Update Build.PL to include all needed libsass sources
Adds missing function cookie
Fixes tests for new libsass version

Percentages and dimensions are replaced by number type.
Add the unit as a string to the second parameter to new.
Updates to latest local libsass version

Rebased my changes to the upstream master branch
Adds defaults for certain SASS variable fields

The unit for numbers should never be undefined.
Adds another check in safe_sv function

This will avoid warnings about the "use of
uninitialized value in subroutine entry".