makefile: revert .c deps to core/config.h again

also add gcov stuff gcda gcno to clean
doc: number (minor)
syntax.y: use simplier SRC_TPL3 macros, document more sig plans (-\* modifiers, attribs)
front/potion.c harmonize fatal error msg
sig-default bytecode vm: use potion_sig_at, extend stack when a default is added

do not clean locals on reentry, clean stack at the beginning.
calling a functions resets pos to 0, and starts again at reentry.
we don't want our locals be cleaned away, esp. with nested functions.