Update to version 3.1.1

This version fixes a regression with regard to tradtional behavior of the
non-standard FreeBSD option "-e". In the previous version "-e quit" caused
bc to exit before any computations had been performed, since all -e option
parameters were concatenated and parsed as a whole, with quit causing the
program to exit as soon as it was parsed. This version parses and executes
commands passed with -e one by one and only exits after all prior commands
have been executed.

This commit is not a SVN merge, since the vendor import had been performed
after the import to contrib. Instead the contents of contrib/bc has been
removed and the new version is copied over unchanged from vendor/bc/dist.