diff: allow turning on textconv explicitly for plumbing
Some history viewers use the diff plumbing to generate diffs rather than going through the "git diff" porcelain. Currently, there is no way for them to specify that they would like to see the text-converted version of the diff.
This patch adds a "--textconv" option to allow such a plumbing user to allow text conversion. The user can then tell the viewer whether or not they would like text conversion enabled.
While it may be tempting add a configuration option rather than requiring each plumbing user to be configured to pass --textconv, that is somewhat dangerous. Text-converted diffs generally cannot be applied directly, so each plumbing user should "opt in" to generating such a diff, either by explicit request of the user or by confirming that their output will not be fed to patch.
Signed-off-by: Jeff King <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>