make shell math operations style more succulent

Convert the style:
	var=$((${var} + 1))
to:
	: $(( var += 1 ))

The latter is easier to read imo.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

sh/functions.sh.in

@@ -8,14 +8,14 @@ RC_GOT_FUNCTIONS="yes"
 
 eindent()
 {
-	EINFO_INDENT=$((${EINFO_INDENT:-0} + 2))
+	: $(( EINFO_INDENT = ${EINFO_INDENT:-0} + 2 ))
 	[ "$EINFO_INDENT" -gt 40 ] && EINFO_INDENT=40
 	export EINFO_INDENT
 }
 
 eoutdent()
 {
-	EINFO_INDENT=$((${EINFO_INDENT:-0} - 2))
+	: $(( EINFO_INDENT = ${EINFO_INDENT:-0} - 2 ))
 	[ "$EINFO_INDENT" -lt 0 ] && EINFO_INDENT=0
 	return 0
 }

sh/rc-mount.sh

@@ -59,7 +59,7 @@ do_unmount()
 						eend 1
 					else
 						local sig="TERM"
-						retry=$(($retry - 1))
+						: $(( retry -= 1 ))
 						[ $retry = 1 ] && sig="KILL"
 						fuser $f_kill$sig -k $f_opts \
 							"$mnt" >/dev/null 2>&1

sh/runtests.sh

@@ -9,17 +9,17 @@ tret=0
 ebegin "Testing yesno()"
 for f in yes YES Yes true TRUE True 1 ; do
 	if ! yesno $f; then
-		tret=$(($tret + 1))
+		: $(( tret += 1 ))
 		echo "!$f!"
 	fi
 done
 for f in no NO No false FALSE False 0 ; do
 	if yesno $f; then
-		tret=$(($tret + 1))
+		: $(( tret += 1 ))
 		echo "!$f!"
 	fi
 done
 eend $tret
-ret=$(($ret + $tret))
+: $(( ret += $tret ))
 
 exit $ret