hideRefs: add support for matching full refs

hideRefs: add support for matching full refs

In addition to matching stripped refs, one can now add hideRefs
patterns that the full (unstripped) ref is matched against. To
distinguish between stripped and full matches, those new patterns
must be prefixed with a circumflex (^).

This commit also removes support for the undocumented and unintended
hideRefs settings ".have" (suppressing all "have" lines) and
"capabilities^{}" (suppressing the capabilities line).

Signed-off-by: Lukas Fleischer <lfleischer@lfos.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>