Fix distcheck by adding back protocol/Makefile.am

5909dddc78 removed protocol/Makefile.am
which meant protocol/wayland.xml no longer got included in the tarball.
Add back protocol/Makefile.am and configure.ac bits and add protocol to
subdirs in Makefile.am to fix this.

Makefile.am

@@ -2,7 +2,7 @@ if BUILD_DOCS
 doc_subdir = doc
 endif
 
-SUBDIRS = src $(doc_subdir) tests cursor
+SUBDIRS = src protocol $(doc_subdir) tests cursor
 
 ACLOCAL_AMFLAGS = -I m4 ${ACLOCAL_FLAGS}
 

configure.ac

@@ -116,5 +116,6 @@ AC_CONFIG_FILES([Makefile
 		 src/wayland-server.pc
 		 src/wayland-client.pc
 		 src/wayland-version.h
+		 protocol/Makefile
 		 tests/Makefile])
 AC_OUTPUT

protocol/Makefile.am

@@ -0,0 +1 @@
+EXTRA_DIST = wayland.xml