More changes to teh way ExplodedArchive works in non-recursive mode

It is sufficient for most purposes (e.g. the ones PropertieLauncher needs)
to only read the META-INF directory (not the whole file tree). So a quick
fix is to make META-INF a special case when initializing non-recursive
entries.

Fixes gh-520

spring-boot-tools/spring-boot-loader/src/test/resources/root/META-INF/spring/application.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+
+</beans>