Klammerset: the @@@klammerset construct, its search path, and const correctness

The @@@klammerset system command formally declares a klammerset — a
named, logically related group of klammer definitions — with an
operative, idempotent declaration (:requires and :files load in order
at the declaration point, relative to the declaring file). A bare
symbol given to ktext -k, kdesc --input, or :requires resolves to
x/x.k on the search path: the document's directory, then
KLAMMERTEXT_KLAMMERSETS, then KLAMMERTEXT_HOME; kdesc --klammerset
lists the available sets. sks/sks.k is the first declared klammerset,
so `-k sks` loads the SKS by name. The engine's lookup classes were
renamed *_set → *_registry to keep the two concepts apart, and the
whole C++ tree now follows standard const-correctness conventions.
tst/ gains klammerset_test.sh (18 cases).

(from dev 64b1abf23e56)

mac/Makefile

@@ -8,9 +8,9 @@ include $(K)/env/makefile.env
 
 # Source files
 BASENAMES := util error locator file argv character ktype katom katom_list \
-             log show command argument argument_set argtype argtype_set \
-             state eval eval_python eval_cpp klammer klammer_set deftype \
-             target target_set machine font_store
+             log show command argument argument_set argtype argtype_registry \
+             state eval eval_python eval_cpp klammer klammer_registry klammerset klammerset_registry deftype \
+             target target_registry machine font_store
 
 SOURCES := $(addsuffix .cpp,$(BASENAMES))
 OBJECTS := $(addsuffix .o,$(BASENAMES))