R=rsc https://codereview.appspot.com/10690044

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.