Merge branch 'ab/conditional-config-with-symlinks'

The recently introduced "[includeIf "gitdir:$dir"] path=..."
mechansim has further been taught to take symlinks into account.
The directory "$dir" specified in "gitdir:$dir" may be a symlink to
a real location, not something that $(getcwd) may return.  In such
a case, a realpath of "$dir" is compared with the real path of the
current repository to determine if the contents from the named path
should be included.

* ab/conditional-config-with-symlinks:
config: match both symlink & realpath versions in IncludeIf.gitdir:*

diff --cc Documentation/config.txt
Simple merge

diff --cc config.c
Simple merge