Merge branch 'nd/wildmatch-double-asterisk'

A pattern with '**' that does not have a slash on either side used
to be an invalid one, but the code now treats such double-asterisks
the same way as two normal asterisks that happen to be adjacent to
each other.

* nd/wildmatch-double-asterisk:
wildmatch: change behavior of "foo**bar" in WM_PATHNAME mode

diff --cc Documentation/gitignore.txt
Simple merge

diff --cc t/t3070-wildmatch.sh
Simple merge