Add support for inch(in) and millimeter(mm) dimensions in dimens.xml

Conflicts:

	src/main/java/com/xtremelabs/robolectric/res/DimenResourceLoader.java
	src/test/java/com/xtremelabs/robolectric/R.java
	src/test/java/com/xtremelabs/robolectric/res/DimenResourceLoaderTest.java
	src/test/resources/res/values/dimens.xml