This bug fix allows some pathological regular
expressions to cause the regexp library to
report a stack overflow (really a stack filling; safe)
but it also fixes the behavior of some common regexps.
It is too hard to satisfy both.
echo SYSSYSR1 | sed 's/SYS.+/sysr1/'
was producing SYSsysr1 instead of sysr1.
Bug was introduced during overflow cleanup earlier this year.
Also bring regexec.c and rregexec.c into sync again.
Also allocate large enough lists in the regexec2/rregexec2 case.
