repo_shell honors git ACLs

* repo_shell uses git_acl.c
* str_has_word returns C99 bool
* git acl filename is set in repo_shell.cfg
* git_acl() accepts const char* args
* git_acl.h doesn't need to include stdbool.h
* git_acl.c manages no default git acl filename
* Use meaningful error message if permission denied due to ACL rule
* repo_shell has -t mode to get git acl function