Add '_' to the allowable characters in a host name.

This does not fix the underscore problem in host names but it moves it from a
Browser issue to a libc issue.

core/java/android/net/WebAddress.java

@@ -54,7 +54,7 @@ public class WebAddress {
     static Pattern sAddressPattern = Pattern.compile(
             /* scheme    */ "(?:(http|HTTP|https|HTTPS|file|FILE)\\:\\/\\/)?" +
             /* authority */ "(?:([-A-Za-z0-9$_.+!*'(),;?&=]+(?:\\:[-A-Za-z0-9$_.+!*'(),;?&=]+)?)@)?" +
-            /* host      */ "([-A-Za-z0-9%]+(?:\\.[-A-Za-z0-9%]+)*)?" +
+            /* host      */ "([-A-Za-z0-9%_]+(?:\\.[-A-Za-z0-9%_]+)*)?" +
             /* port      */ "(?:\\:([0-9]+))?" +
             /* path      */ "(\\/?.*)?");