add interfaces.hh to Makefile.am again (otherwise missing from tarball)

[[Imported from SVN: r5447]]

common/.gitignore

@@ -3,5 +3,6 @@ Makefile.in
 .deps
 .libs
 *.lo
+*.swp
 libcommon.la
-semantic.cache
\ No newline at end of file
+semantic.cache

common/Makefile.am

@@ -23,7 +23,8 @@ commoninclude_HEADERS = dlist.cc alignment.hh \
   mpicollectivecommunication.hh geometrytype.hh utility.hh \
   bartonnackmanifcheck.hh binaryfunctions.hh lru.hh fassign.hh \
   static_assert.hh smallobject.hh version.hh \
-  float_cmp.cc float_cmp.hh
+  float_cmp.cc float_cmp.hh \
+  interfaces.hh
 
 if EXPRESSIONTEMPLATES
 commoninclude_HEADERS += exprtmpl.hh exprtmpl/scalar.inc exprtmpl/exprexpr.inc