fetch: prefer suffix substitution in compact fetch.output

fetch: prefer suffix substitution in compact fetch.output

I have a remote named "jch" and it has a branch with the same name. And
fetch.output is set to "compact". Fetching this remote looks like this

 From https://github.com/gitster/git
  + eb7fd39f6b...835363af2f jch                -> */jch  (forced update)
    6f11fd5edb..59b12ae96a  nd/config-move-to  -> jch/*
  * [new branch]            nd/diff-parseopt   -> jch/*
  * [new branch]            nd/the-index-final -> jch/*

Notice that the local side of branch jch starts with "*" instead of
ending with it like the rest. It's not exactly wrong. It just looks
weird.

This patch changes the find-and-replace code a bit to try finding prefix
first before falling back to strstr() which finds a substring from left
to right. Now we have something less OCD

 From https://github.com/gitster/git
  + eb7fd39f6b...835363af2f jch                -> jch/*  (forced update)
    6f11fd5edb..59b12ae96a  nd/config-move-to  -> jch/*
  * [new branch]            nd/diff-parseopt   -> jch/*
  * [new branch]            nd/the-index-final -> jch/*

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>