Parse unknown tags as inline elements that can contain blocks.

Ensures <p><custom>Test</custom></p> parses like that, and not
<p></p><custom>Test</custom>.

Closes #1

src/main/java/org/jsoup/parser/Tag.java

@@ -49,9 +49,11 @@ public static Tag valueOf(String tagName) {
         synchronized (tags) {
             Tag tag = tags.get(tagName);
             if (tag == null) {
-                // not defined: create default
+                // not defined: create default; go anywhere, do anything! (incl be inside a <p>)
                 tag = new Tag(tagName);
                 tag.setAncestor(defaultAncestor.tagName);
+                tag.isBlock = false;
+                tag.canContainBlock = true;
             }
             return tag;
         }

src/test/java/org/jsoup/org/jsoup/safety/CleanerTest.java

@@ -74,4 +74,10 @@ public class CleanerTest {
         String cleanHtml = Jsoup.clean(h, Whitelist.relaxed());
         assertEquals("<a>XSS</a>", cleanHtml);
     }
+
+    @Test public void testDropsUnknownTags() {
+        String h = "<p><custom foo=true>Test</custom></p>";
+        String cleanHtml = Jsoup.clean(h, Whitelist.relaxed());
+        assertEquals("<p>Test</p>", cleanHtml);
+    }
 }

src/test/java/org/jsoup/parser/ParserTest.java

@@ -187,6 +187,13 @@ public class ParserTest {
         assertEquals("qux", foos.last().attr("title"));
         assertEquals("there", foos.last().text());
     }
+
+    @Test public void handlesUnknownInlineTags() {
+        String h = "<p><cust>Test</cust></p><p><cust><cust>Test</cust></cust></p>";
+        Document doc = Jsoup.parseBodyFragment(h);
+        String out = doc.body().html();
+        assertEquals(h, TextUtil.stripNewlines(out));
+    }
 
     @Test public void handlesEmptyBlocks() {
         String h = "<div id=1/><div id=2><img /></div>";