Add symbolic names for zero (ROOT,BACK) and fix up for non-recursive make.
Complete the fix for non-recursive make.
Merge https://github.com/mischasan/aho-corasick

Conflicts:
	GNUmakefile
tweak GNUmakefile,rules.mk
Merge https://github.com/mischasan/aho-corasick
rules.mk consistent with all other projects