An output policy for the three commands, and @cond as a true special form

A snapshot of the development tree.  The substantial changes since the last one:

COMMAND OUTPUT POLICY.  The three commands display text in exactly three cases,
and each owns a stream: LOGGING under "-v" greater than 0 and an ERROR before
termination go to STDERR; OUTPUT THE USER ASKED FOR goes to STDOUT.  For ktext
that output is a document, so "ktext doc.kt -d | ..." is now safe -- logging
used to share the stream and land inside the document.  A bare command prints
its usage and succeeds rather than failing.  Colour is emitted only to a
terminal, per stream, and NO_COLOR is honoured.

"-v 1" reports every decision whose outcome you could not have read off your own
input: the klammerset that was loaded and from which file, a font's directory, a
":files" name's file, how "-o" was expanded.  Higher levels are the trace.

The commands no longer warn and continue: an anomaly is an error, described with
its location.  Two exceptions remain, each for a stated reason -- a condition
that is expected and temporary by design, and a judgment that is a heuristic
rather than exact.

@cond IS NOW A TRUE SPECIAL FORM, resolved at APPLICATION time rather than when
the file is read.  Two consequences for a writer:

  * a state variable reaches the predicate.  "@@@state Flag :value true @@@
    @cond *Flag* | T | F @" renders "T"; it used to see the literal "*Flag*" and
    silently take the false branch.  The document now behaves like a klammer
    body, whose arguments are bound before its conditionals are decided.
  * nothing in a discarded branch happens -- it is not read, not evaluated, not
    expanded.  An @eval in the branch not taken used to run anyway.

Its predicate relation is total and strict: true, True, 1; false, False, 0, and
empty; anything else is an error at the @cond rather than silently false.

@eval REACHING OUTSIDE.  ":shell" and ":haskell" now keep the command's standard
error out of the document (it appears under "-v 1") and treat a nonzero exit as
an error naming what the command reported.  A command that exits nonzero on
purpose -- "grep" finding no match -- says so with "|| true".

KLAMMER SETS.  Several combine: "--klammersets a b c" loads all three in the
order given, sharing one namespace, with the definition modes deciding
collisions.  "none" means none and may not be combined with other symbols.  A
klammerset with symbol X is declared in a file X/X.k, which is what lets two
sets require the same third set without loading it twice.

TESTS.  Four new suites: the kdiag command's interface, the @eval primitive's
contract with the outside world, and verbosity at both tiers.  Three suites
that could not run on macOS at all now do.

Assembled from dev commit 6c8ee6c22fca.

mac/klammerset_registry.h

@@ -19,12 +19,25 @@ public:
     // (typically reached through :requires) is skipped, not an error.
     std::optional<Klammerset> add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms);
     void check_symbol(const std::string& symbol, const Locator& loc) const;
+    // Symbol X must be declared in X/X.k, so that the symbol is a function of
+    // the path and the already-loaded guard can run before a file is read.
+    void check_declaring_file(const std::string& symbol, const Locator& loc) const;
 
     bool has(const std::string& symbol) const;
     Klammerset get(const std::string& symbol, const Locator& loc) const;
 
     std::string describe(int margin=2, bool long_format=false) const;
 
+    // Record what a set actually opened (see Klammerset::m_loaded_files).
+    void set_loaded_files(const std::string& symbol, const strings_t& files);
+
+    // Every file every registered klammerset read.  A klammer whose
+    // definitions all come from these was supplied by a klammerset; one with
+    // a definition elsewhere was defined by the input -- which is the
+    // distinction "kdesc -i" needs, since it loads a klammerset in order to
+    // analyse a file without wanting to LIST the klammerset's own klammers.
+    strings_t loaded_files() const;
+
     std::map<std::string, Klammerset> m_klammersets {};
     std::vector<std::string> m_symbols {};
     Parameter_set m_parameters {};
@@ -59,5 +72,5 @@ fs::path resolve_klammerset_symbol(
 
 // The symbols available on the search path, with provenance; a symbol
 // found again in a later directory is marked as shadowed.  For
-// kdesc --klammerset.
+// kdesc --klammersets.
 std::string describe_klammerset_search(const std::string& local_dir, int margin=2);