Update to 4.3.12

Update to 4.3.12

Changes:
Improved error handling in POSIX emulation, ${NAME:OFFSET:LENGTH}
syntax supports negative LENGTHs, new parameter expansion flag
(g:opts:) which escapes sequences like the echo and print builtins,
the region_highlight array is now updated dynamically as the command
line is edited and the zsh/parameter module has a new array $usergroups
which contains the names of system groups.