do not use possibly absent 'which' command

common/base.sh

@@ -1,3 +1,17 @@
+which()
+{
+	# on some systems 'which' command is considered deprecated and not installed by default
+	# 'command -v' replacement does not work exactly the same way. it outputs shell aliases if present
+	# $1 - executable name
+	local IFS=:
+	for p in $PATH; do
+	    [ -x "$p/$1" ] && {
+		echo "$p/$1"
+		return 0
+	    }
+	done
+	return 1
+}
 exists()
 {
 	which "$1" >/dev/null 2>/dev/null