Refine command line option preprocessor and add tests for #8956.

The substantive change here is the `-strue` will now work
instead of being interpreted as `-s -true`.

This is somewhat ad hoc, but I don't think we'll ever have
an output format named `rue`, so it's probably okay.

test/command/8956.md

@@ -1,10 +1,12 @@
 ```
-% pandoc -itslidy
+% pandoc -iNtslidy
+# One
+
 - one
 - two
 ^D
-<div class="slide section level6">
-
+<div id="one" class="slide section level1" number="1">
+<h1><span class="header-section-number">1</span> One</h1>
 <ul class="incremental">
 <li>one</li>
 <li>two</li>
@@ -18,13 +20,16 @@
 	after tab
 ```
 ^D
+Pandoc
+  Meta { unMeta = fromList [] }
+  [ CodeBlock ( "" , [] , [] ) "\tafter tab" ]
 ````
 
 ```
-% pandoc -strue
+% pandoc -sfalse
+hi
 ^D
-2> Could not find data file templates/default.rue
-=> 97
+<p>hi</p>
 ```
 
 ```
@@ -34,3 +39,10 @@ hi
 <p>hi</p>
 ```
 
+```
+% pandoc --standalone=FALSE
+hi
+^D
+<p>hi</p>
+```
+