merge-recursive: options to ignore whitespace changes

merge-recursive: options to ignore whitespace changes

Add support for merging with ignoring line endings (specifically
--ignore-space-at-eol) when using recursive merging.  This is
as a strategy-option, so that you can do:

	git merge --strategy-option=ignore-space-at-eol <branch>

and

	git rebase --strategy-option=ignore-space-at-eol <branch>

This can be useful for coping with line-ending damage (Xcode 3.1 has a
nasty habit of converting all CRLFs to LFs, and VC6 tends to just use
CRLFs for inserted lines).

The only option I need is ignore-space-at-eol, but while at it,
include the other xdiff whitespace options (ignore-space-change,
ignore-all-space), too.

[jn: with documentation]

Signed-off-by: Justin Frankel <justin@cockos.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>