do reverse of a bytecode in lookbehinds
backtracking matcher works with reversed bytecode
ditto with Thompson matcher
cleanup to keep lookahead/lookbehind more in sync for future

Fix 64 bit issues, remove useless debug hook
fix broken indention, detab
Merge pull request #1484 from blackwhale/kill-back-eval

std.regex: First step to lookbehind in ctRegex