add support for a common shell include file, which is evaluated for every make shell call, simplify variable passing to the shell with shvar and shexport templates, use Package/<pkgname>/config for adding config.in data

git-svn-id: svn://svn.openwrt.org/openwrt/branches/buildroot-ng/openwrt@5014 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/shell.sh

@@ -0,0 +1,15 @@
+getvar() {
+	eval "echo \"\${$1}\""
+}
+
+var2file() {
+	local var
+	eval "var=\"\${$1}\""
+	if [ -n "$var" ]; then echo "$var" > "$2"; fi
+}
+
+isset() {
+	local var
+	eval "var=\"\${$1}\""
+	[ -n "$var" ]
+}