Fix typo, fix make dist

As for make distclean, I can't think of any solution but moving vlc.c out of
src/ (I know it sucks, but you don't want to rewrite automake, do you?).

mozilla/Makefile.am

@@ -17,7 +17,7 @@ SOURCES_mozilla_common = \
 	support/classinfo.h
 
 DIST_sources = $(SOURCES_mozilla_common) \
-	support/npwin.cpp support/npmac.cpp support/npunix.cpp
+	support/npwin.cpp support/npmac.cpp support/npunix.c
 
 if BUILD_SHARED
 LIBRARIES_libvlc_pic = -Wl,-rpath '$(libdir)' -L$(top_builddir)/src -lvlc