Add support for TLS_FALLBACK_SCSV

Backport of commits:

external/conscrypt: 8d7e23e117da591a8d48e6bcda9ed6f58ff1a375
libcore: e6a6e935e98f426c7000b2bf4086f87101f4441c
libcore: 957ec8b09833e1c2f2c21380e53c13c9962e6b3e

Plus additional changes to:
luni/src/main/java/org/apache/harmony/xnet/provider/jsse/OpenSSLServerSocketImpl.java
luni/src/main/java/org/apache/harmony/xnet/provider/jsse/OpenSSLSocketImpl.java
luni/src/test/java/libcore/java/net/URLConnectionTest.java
luni/src/test/java/org/apache/harmony/xnet/provider/jsse/CipherSuiteTest.java
support/src/test/java/libcore/java/security/StandardNames.java

to account for KitKat differences.

Bug: 17750026
Change-Id: Ic6e9474275bc3ffec3b5c2d6df1f8d6ffe77bff8
Allow "_" in URIs.

Note that this is contrary to RFC-2396, which only allows alphanumeric
characters and hyphens. We need this change because internet hosts out
there clearly don't care enough about standards.

bug: 18023709

Change-Id: I9459f58d49ccc68af887a14c889eaa60b6c3150d