Do not force targets to be SECONDARY

In SV 43677 we forced targets to be secondary if we found an
intermediate file that was listed as a prerequisite of another
target.  This overrides .INTERMEDIATE settings, so doesn't work.
Now that we have an is_explicit flag in targets, use that instead.

* src/implicit.c (pattern_search): Remove setting of secondary.
Preserve the value of the is_explicit flag when creating a new
file target, and consider it when setting the intermediate flag.
* tests/scripts/features/patternrules: Add a test w/out INTERMEDIATE
* tests/scripts/targets/INTERMEDIATE: Add a test with INTERMEDIATE

tests/scripts/features/patternrules

@@ -444,5 +444,17 @@ hello.tsk:
 
 unlink('hello.tsk');
 
+# A target explicitly listed as a prerequisite of a pattern rule, is still
+# considered mentioned and "ought to exist".
+
+run_make_test(q!
+1.all: 1.q ; touch $@
+%.q: 1.r ; touch $@
+%.r: ; touch $@
+!,
+              '', "touch 1.r\ntouch 1.q\ntouch 1.all\n");
+
+unlink('1.all', '1.q', '1.r');
+
 # This tells the test driver that the perl test script executed properly.
 1;