[ufo] 'make install' installs .pir files

Reversed moritz++'s decision to install the .pm files per default and the
.pir files only secondarily. The .pir files are the built resource to be
installed, and the .pm files secondary. It might make sense to add the latter
for documentation-browsing reasons, etc. Remains to be seen what pls will
do by default.

ufo

@@ -117,20 +117,19 @@ clean:
 test: all
 \tenv PERL6LIB=\$(PERL6LIB) prove -e '\$(PERL6)' -r --nocolor t/]);
 
-
 sub write-install($extension?) {
     for @sources -> $s {
         my $file = defined $extension
                     ?? $s.subst(rx{\.pm6?$}, '.' ~ $extension)
-                        !! $s;
+                    !! $s;
         $makefile.say("\tinstall -D $file ~/.perl6/$file");
     }
 }
 
 $makefile.say(q[]);
-$makefile.say(q[install:]);
-write-install();
+$makefile.say(q[install: all]);
+write-install('pir');
 
 $makefile.say(q[]);
-$makefile.say(q[install-pir: all]);
-write-install('pir');
+$makefile.say(q[install-src:]);
+write-install();