completion: normalize increment/decrement style

The style used for incrementing and decrementing variables was fairly
inconsistenty and was normalized to use x++, or ((x++)) in contexts
where the former would otherwise be interpreted as a command. This is a
bash-ism, but for obvious reasons this script is already bash-specific.

Signed-off-by: Philip Jägenstedt <philip@foolip.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -137,7 +137,7 @@ __git_ps1_show_upstream ()
 			svn_upstream=${svn_upstream[ ${#svn_upstream[@]} - 2 ]}
 			svn_upstream=${svn_upstream%@*}
 			local n_stop="${#svn_remote[@]}"
-			for ((n=1; n <= n_stop; ++n)); do
+			for ((n=1; n <= n_stop; n++)); do
 				svn_upstream=${svn_upstream#${svn_remote[$n]}}
 			done
 
@@ -166,10 +166,8 @@ __git_ps1_show_upstream ()
 			for commit in $commits
 			do
 				case "$commit" in
-				"<"*) let ++behind
-					;;
-				*)    let ++ahead
-					;;
+				"<"*) ((behind++)) ;;
+				*)    ((ahead++))  ;;
 				esac
 			done
 			count="$behind	$ahead"
@@ -727,7 +725,7 @@ __git_complete_remote_or_refspec ()
 	local cur_="$cur" cmd="${words[1]}"
 	local i c=2 remote="" pfx="" lhs=1 no_complete_refspec=0
 	if [ "$cmd" = "remote" ]; then
-		c=$((++c))
+		((c++))
 	fi
 	while [ $c -lt $cword ]; do
 		i="${words[c]}"
@@ -746,7 +744,7 @@ __git_complete_remote_or_refspec ()
 		-*) ;;
 		*) remote="$i"; break ;;
 		esac
-		c=$((++c))
+		((c++))
 	done
 	if [ -z "$remote" ]; then
 		__gitcomp_nl "$(__git_remotes)"
@@ -986,7 +984,7 @@ __git_find_on_cmdline ()
 				return
 			fi
 		done
-		c=$((++c))
+		((c++))
 	done
 }
 
@@ -997,7 +995,7 @@ __git_has_doubledash ()
 		if [ "--" = "${words[c]}" ]; then
 			return 0
 		fi
-		c=$((++c))
+		((c++))
 	done
 	return 1
 }
@@ -1120,7 +1118,7 @@ _git_branch ()
 		-d|-m)	only_local_ref="y" ;;
 		-r)	has_r="y" ;;
 		esac
-		c=$((++c))
+		((c++))
 	done
 
 	case "$cur" in
@@ -2574,7 +2572,7 @@ _git_tag ()
 			f=1
 			;;
 		esac
-		c=$((++c))
+		((c++))
 	done
 
 	case "$prev" in
@@ -2627,7 +2625,7 @@ _git ()
 		--help) command="help"; break ;;
 		*) command="$i"; break ;;
 		esac
-		c=$((++c))
+		((c++))
 	done
 
 	if [ -z "$command" ]; then