use git log --follow on history and blame

Show complete file history even when file has been renamed.

Replaces https://github.com/gitlabhq/gitlabhq/pull/8188
Related to https://github.com/gitlabhq/gitlabhq/pull/7417, https://github.com/gitlabhq/gitlabhq/pull/3502, https://github.com/gitlabhq/gitlabhq/issues/6966, https://github.com/gitlabhq/gitlabhq/issues/1954
Fixes https://github.com/gitlabhq/gitlabhq/issues/7832
Closes https://github.com/gitlabhq/gitlab_git/pull/35
For future usage as suggested by @mr-vinn at https://github.com/gitlabhq/gitlab_git/pull/35#issuecomment-60769195.