Merge branch 'nd/completion-negation'

Continuing with the idea to programmatically enumerate various
pieces of data required for command line completion, the codebase
has been taught to enumerate options prefixed with "--no-" to
negate them.

* nd/completion-negation:
completion: collapse extra --no-.. options
completion: suppress some -no- options
parse-options: option to let --git-completion-helper show negative form

diff --cc builtin/checkout.c
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc t/t9902-completion.sh
Simple merge