completion: improve ls-remote output filtering in __git_refs()

The remote-handling part of __git_refs() has a nice for loop and state
machine case statement to iterate over all words from the output of
'git ls-remote' to identify object names and ref names.  Since each
line in the output of 'git ls-remote' consists of an object name and a
ref name, we can do more effective filtering by using a while-read
loop and letting bash's word splitting take care of object names.
This way the code is easier to understand and the loop will need only
half the number of iterations than before.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -580,7 +580,7 @@ __git_tags ()
 # by checkout for tracking branches
 __git_refs ()
 {
-	local i is_hash=y dir="$(__gitdir "${1-}")" track="${2-}"
+	local i hash dir="$(__gitdir "${1-}")" track="${2-}"
 	local format refs
 	if [ -d "$dir" ]; then
 		case "$cur" in
@@ -616,12 +616,12 @@ __git_refs ()
 		fi
 		return
 	fi
-	for i in $(git ls-remote "$dir" HEAD ORIG_HEAD 'refs/tags/*' 'refs/heads/*' 'refs/remotes/*' 2>/dev/null); do
-		case "$is_hash,$i" in
-		y,*) is_hash=n ;;
-		n,*^{}) is_hash=y ;;
-		n,refs/*) is_hash=y; echo "${i#refs/*/}" ;;
-		n,*) is_hash=y; echo "$i" ;;
+	git ls-remote "$dir" HEAD ORIG_HEAD 'refs/tags/*' 'refs/heads/*' 'refs/remotes/*' 2>/dev/null | \
+	while read hash i; do
+		case "$i" in
+		*^{}) ;;
+		refs/*) echo "${i#refs/*/}" ;;
+		*) echo "$i" ;;
 		esac
 	done
 }