Doesn't set mark at where search started like I-search

[louy2]

It is really convenient for navigation to have a mark at where the search initiated. I-search had this so I was expecting it, but it seems not the case. If I missed where it is please pardon me.

[syohex]

helm-ag uses own mark and you can pop by helm-ag-pop-stack. Marks are frequently overwritten by many emacs commands. And it is difficult to use emacs mark as we expect, so I decide to use own mark in helm-ag.