Make 'dist-hook' targets, which copy the .spec file into $(distdir),

Make 'dist-hook' targets, which copy the .spec file into $(distdir), depend upon the
.spec file, so that the .spec file will be regenerated when a previously-compiled tree
is 'dist'd with a new version number.

Makefile.am

@@ -30,7 +30,7 @@ stamp-gc-h: config.status
 	CONFIG_FILES= CONFIG_HEADERS= CONFIG_OTHER=glibtop-config.h ./config.status
 	echo timestamp > stamp-gc-h
 
-dist-hook:
+dist-hook: libgtop.spec
 	cp libgtop.spec $(distdir)
 
 release: