This is a big redesign of failure-stack and register handling, prompted

This is a big redesign of failure-stack and register handling, prompted
by bugs revealed when trying to add shy-groups.  Overall, what happened
is that loops are now structured a little differently, groups can be
shy and the code is a little simpler.

(enum re_opcode_t): Remove jump_past_alt, maybe_pop_jump,
push_dummy_failure and dumy_failure_jump.
Add on_failure_jump_(exclusive, loop and smart).
Also fix the comment for (start|stop)_memory since they now only take
one argument (the second has becomes unnecessary).
(print_partial_compiled_pattern): Adjust for changes in re_opcode_t.
(print_compiled_pattern): Use %ld to printf long ints and flush to make
debugging a little easier.
(union fail_stack_elt): Make the integer unsigned.
(struct fail_stack_type): Add a `frame' element.
(INIT_FAIL_STACK): Init `frame' as well.
(POP_PATTERN_OP): New macro for re_compile_fastmap.
(DEBUG_PUSH, DEBUG_POP): Remove.
(NUM_REG_ITEMS): Remove.
(NUM_NONREG_ITEMS): Adjust.
(FAILURE_PAT, FAILURE_STR, NEXT_FAILURE_HANDLE, TOP_FAILURE_HANDLE):
New macros for the cycle detection.
(ENSURE_FAIL_STACK): New macro for PUSH_FAILURE_(REG|POINT).
(PUSH_FAILURE_REG, POP_FAILURE_REG, CHECK_INFINITE_LOOP): New macros.
(PUSH_FAILURE_POINT): Don't push registers any more.
The pattern address pushed is not the destination of the jump
but the source of it instead.
(NUM_FAILURE_ITEMS): Remove.
(POP_FAILURE_POINT): Adapt to the new stack structure (i.e. pop
registers before the actual failure point).
Don't hardcode any meaning for str==NULL anymore.
(union register_info_type, REG_MATCH_NULL_STRING_P, IS_ACTIVE)
(MATCHED_SOMETHING, EVER_MATCHED_SOMETHING, SET_REGS_MATCHED): Remove.
(REG_UNSET_VALUE): Use NULL (why not?).
(compile_range): Remove declaration since it doesn't exist.
(struct compile_stack_elt_t): Remove inner_group_offset.
(old_reg(start|end), reg_info, reg_dummy, reg_info_dummy): Remove.
(regex_grow_registers): Remove dead code.
(FIXUP_ALT_JUMP): New macro.
(regex_compile): Add shy-groups
Change loops to use	on_failure_jump_smart&jump instead of
on_failure_jump&maybe_pop_jump.
Change + loops to eliminate the initial (dummy_failure_)jump.
Remove c1_base (looks like unused variable to me).
Use `jump' instead of `jump_past_alt' and don't bother with
push_dummy_failure in alternatives since it is now unnecessary.
Use FIXUP_ALT_JUMP.
Eliminate a useless `#ifdef emacs' for (re)allocating the stack.
(re_compile_fastmap): Remove dead variables i and num_regs.
Exit from loop when bufp->can_be_null rather than jumping to `done'.
Avoid jumping backwards so as to ensure termination.
Use PATTERN_STACK_EMPTY and POP_PATTERN_OP.
Improved handling of backreferences.
Remove dead code in handling of `anychar'.
(skip_noops, mutually_exclusive_p): New functions taken from the
handling of `maybe_pop_jump' in re_match_2_internal.
Slightly improve mutually_exclusive_p to handle ".+\n".
((lowest|highest)_active_reg, NO_(LOWEST|HIGHEST)_ACTIVE_REG)
Remove.
(re_match_2_internal): Use %p instead of 0x%x when printf'ing ptrs.
Don't SET_REGS_MATCHED anymore.  Remove many dead variables.
Push register (in `start_memory') on the stack rather than storing it
in old_reg(start|end).
Remove the cycle detection from `stop_memory', replaced by the use
of on_failure_jump_loop for greedy loops.
Add code for the new on_failure_jump_<foo>.
Remove ad-hoc code in `on_failure_jump' to push more registers
in the case of a loop.
Take out code from `maybe_pop_jump' into separate functions and
adapt it to the semantics of `on_failure_jump_smart'.
Remove jump_past_alt, dummy_failure_jump and push_dummy_failure.
Remove dummy_failure handling and handling of `failures to jump
to on_failure_jump' (this last one was already dead code, it seems).
((group|alt|common_op)_match_null_string_p): Remove.