Merge branch 'jc/am-i-v-fix' into maint

The "v(iew)" subcommand of the interactive "git am -i" command was
broken in 2.6.0 timeframe when the command was rewritten in C.

* jc/am-i-v-fix:
  am -i: fix "v"iew
  pager: factor out a helper to prepare a child process to run the pager
  pager: lose a separate argv[]