Distribute viratomic.h

Since cbcb1983 we need viratomic.h in
the distributed tarball as well. This fixes "make distcheck".

src/Makefile.am

@@ -52,6 +52,7 @@ augeastest_DATA =
 # These files are not related to driver APIs. Simply generic
 # helper APIs for various purposes
 UTIL_SOURCES =							\
+		util/viratomic.h				\
 		util/bitmap.c util/bitmap.h			\
 		util/buf.c util/buf.h				\
 		util/command.c util/command.h			\