add support for building libtls

Use './configure --enable-libtls' to build the library and install the
associated manpages. Note that the API and ABI of this library may
change still, though feedback is welcome.

ok deraadt@ jsing@ tedu@

.gitignore

@@ -87,12 +87,16 @@ INSTALL
 crypto/Makefile.am
 include/openssl/Makefile.am
 ssl/Makefile.am
+tls/Makefile.am
 apps/Makefile.am
 tests/Makefile.am
 
 ssl/*.c
 ssl/*.h
+tls/*.c
+tls/*.h
 include/pqueue.h
+include/tls.h
 include/openssl/*.h
 include/openssl/*.he
 apps/*.c