fixed small bug in plumedcheck

The used modules were not detected correctly on travis probably due to
some settings for the cd option. This was harmless since the list of used
modules was not checked indeed.

src/maketools/plumedcheck

@@ -210,7 +210,7 @@ BEGINFILE{
         sub("/[^/]*$","",path);
 # an explicit cd is required since the command might be run from a different directory
         system("cd " path "; make show_used_modules 2>/dev/null > " tempfile)
-        if(getline < tempfile >0 && $1=="used_modules") for(i=2;i<=NF;i++) used_modules[module][$i]=1
+        while(getline < tempfile >0) if($1=="used_modules") for(i=2;i<=NF;i++) used_modules[module][$i]=1
         close(tempfile)
         system("rm " tempfile)
         used_modules_here=""