Merge branch 'sr/log-SG-no-textconv'

"git log -S/-G" started paying attention to textconv filter, but
there was no way to disable this.  Make it honor --no-textconv
option.

* sr/log-SG-no-textconv:
  diffcore-pickaxe: unify code for log -S/-G
  diffcore-pickaxe: fix leaks in "log -S<block>" and "log -G<pattern>"
  diffcore-pickaxe: port optimization from has_changes() to diff_grep()
  diffcore-pickaxe: respect --no-textconv
  diffcore-pickaxe: remove fill_one()
  diffcore-pickaxe: remove unnecessary call to get_textconv()