Allow git-filter-branch to process large repositories with lots of branches.

A recommended way to move trees between repositories is to use
git-filter-branch to revise the history for a single tree:

However, this can lead to "argument list too long" errors when the
original repository has many retained branches (>6k)

    /usr/local/git/libexec/git-core/git-filter-branch: line 270:
    /usr/local/git/libexec/git-core/git: Argument list too long
    Could not get the commits

Saving the output from rev-parse and feeding it into rev-list from
its standard input avoids this problem, since the rev-parse output
is not processed as a command line argument.

Signed-off-by: Lee Carver <Lee.Carver@servicenow.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-filter-branch.sh

@@ -255,7 +255,7 @@ else
 	remap_to_ancestor=t
 fi
 
-rev_args=$(git rev-parse --revs-only "$@")
+git rev-parse --revs-only "$@" >../parse
 
 case "$filter_subdir" in
 "")
@@ -268,7 +268,7 @@ case "$filter_subdir" in
 esac
 
 git rev-list --reverse --topo-order --default HEAD \
-	--parents --simplify-merges $rev_args "$@" > ../revs ||
+	--parents --simplify-merges --stdin "$@" <../parse >../revs ||
 	die "Could not get the commits"
 commits=$(wc -l <../revs | tr -d " ")