Fix grouping of contributors by email in graph.

Fixes #3254 (closed).

mentioned in issue #3254 (closed)

mentioned in issue #3180 (closed)

Added 357 commits:

• bb8b6f38...1c040b3f - 356 commits from branch master
• 7b014338 - Merge branch 'master' into contributor-graph-by-email

Reassigned to @rspeicher

cc @rspeicher The merge conflict seems to be bogus.

mentioned in commit 354f2440

Status changed to merged

Picked into 8-2-stable.

mentioned in commit 17a0cd46