Fixed bug #59 "bogus 'yyaccept' in '-c' mode".

Fixed bug #59 "bogus 'yyaccept' in '-c' mode".

We have one 'yyaccept' initialization per re2c block. Each block
consists of one or more DFA (multiple DFA in '-c' mode in case of
multiple conditions). Each DFA may or may not use 'yyaccept'
(that is, save 'yyaccept' in some states and have a dispatch state
based on saved 'yyaccept' value).

Description of the bug: in '-c' mode, sometimes a DFA would have
states that save 'yyaccept', but no dispatch state that uses that
saved values. DFA didn't actually need 'yyaccept' (all the
assignments vanished if other conditions that need 'yyaccept' were
removed).

The essence of the bug: re2c decided whether to output 'yyaccept'
related stuff on a per-block basis: for multiple conditions in the
same block, the same decision was made (if any condition needed
'yyaccept', all of them would to output it).

The fix: 'yyaccept' initialization should be done on a per-block
basis, while assignments to 'yyaccept' should be done on a per-DFA
basis. Also, 'yyaccept' initialization must be delayed, while
assignments to 'yyaccept' must not.

Note: we may consider per-DFA 'yyaccept' initialization (have a
local 'yyaccept' variable per DFA). This wouldn't conflict with '-f'
switch (as it might seem) as long as we name all the variables
'yyaccept' and don't generate any 'yyaccept' initializations with '-f'.