Make "git grep" and "git show" pay attention to --textconv when
dealing with blob objects.
* mg/more-textconv:
grep: honor --textconv for the case rev:path
grep: allow to use textconv filters
t7008: demonstrate behavior of grep with textconv
cat-file: do not die on --textconv without textconv filters
show: honor --textconv for blobs
diff_opt: track whether flags have been set explicitly
t4030: demonstrate behavior of show with textconv
4197361e39