Create parse warning if VERSION property is missing

#150

src/main/java/ezvcard/io/text/VCardReader.java

@@ -250,6 +250,22 @@ public void onComponentEnd(String name, Context context) {
 			VCardStack.Item item = stack.pop();
 			assignLabels(item.vcard, item.labels);
 
+			/*
+			 * Is the version property completely absent?
+			 * 
+			 * If a VERSION property with an invalid value is present, the
+			 * property is parsed as a RawProperty and a different warning is
+			 * generated by vinnie.
+			 */
+			if (!item.validVersionPropertyFound && item.vcard.getExtendedProperty("VERSION") == null) {
+				//@formatter:off
+				warnings.add(new ParseWarning.Builder()
+					.message(39, item.vcard.getVersion())
+					.build()
+				);
+				//@formatter:on
+			}
+
 			if (stack.isEmpty()) {
 				context.stop();
 			}
@@ -423,7 +439,10 @@ private void handleLabelParameter(VCardProperty property) {
 		public void onVersion(String value, Context vobjectContext) {
 			VCardVersion version = VCardVersion.valueOfByStr(value);
 			context.setVersion(version);
-			stack.peek().vcard.setVersion(version);
+
+			VCardStack.Item item = stack.peek();
+			item.vcard.setVersion(version);
+			item.validVersionPropertyFound = true;
 		}
 
 		public void onWarning(Warning warning, VObjectProperty property, Exception thrown, Context vobjectContext) {
@@ -572,6 +591,7 @@ public boolean isEmpty() {
 		private static class Item {
 			public final VCard vcard;
 			public final List<Label> labels;
+			public boolean validVersionPropertyFound = false;
 
 			public Item(VCard vcard, List<Label> labels) {
 				this.vcard = vcard;

src/main/resources/ezvcard/messages.properties

@@ -77,6 +77,7 @@ parse.37=Line {0}: {2}
 parse.22=Property has requested that it be skipped: {0}
 parse.25=Property value could not be parsed: {0}
 #parse.26=Problem parsing property in nested vCard: {0} #removed in 0.10.2-SNAPSHOT
+parse.39=VERSION property missing. Defaulting to version {0}.
 
 #plain-text
 parse.23=The property''s character encoding ("{0}") is not supported by this system.  {1} will be used instead.

src/test/java/ezvcard/io/text/VCardReaderTest.java

@@ -835,6 +835,20 @@ public void value_parameter() throws Exception {
 			assertNoMoreVCards(reader);
 		}
 	}
+
+	@Test
+	public void missing_version() throws Exception {
+		//@formatter:off
+		VCardAsserter asserter = read(
+		"BEGIN:VCARD\r\n" +
+		"END:VCARD\r\n"
+		);
+
+		asserter.next(V2_1); //default to 2.1
+		asserter.warnings(39);
+		asserter.done();
+		//@formatter:on
+	}
 
 	@Test
 	public void invalid_version() throws Exception {