[tracker] (6 commits) Non-fast-forward update to branch wip/carlosg/sparql-fixes

[Carlos Garnacho <carlosg src gnome org>]

The branch 'wip/carlosg/sparql-fixes' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  058d2c2... libtracker-data: Check for variables in the most direct con
  be7b0bb... tests: Add test for service in subselect
  50994b2... libtracker-data: Handle empty GroupGraphPattern
  9d7a291... tests: Add test for empty group patterns
  76dfb94... libtracker-sparql: Differentiate property path elements by 
  bd372e7... tests: Add tests for property paths used from several graph

Commits added to the branch:

  ed9a786... libtracker-data: Check for variables in the most direct con
  6b2a57d... tests: Add test for service in subselect
  51cd345... libtracker-data: Handle empty GroupGraphPattern
  d881546... tests: Add test for empty group patterns
  e8309cb... libtracker-sparql: Differentiate property path elements by 
  dce9bc2... tests: Add tests for property paths used from several graph