It appears that use of the `git:branch-unique(*)` causes a number of arc commands to fail on CentOS/RHEL 6, due to its version of Git (1.7.1) not supporting the `-c` argument.
For example,
`$ arc which --base 'git:branch-unique(origin/master)' --trace` shows that arc tries to execute:
`git -c column.ui=never -c color.ui=never branch --contains 'b500ca6e1b1943ff88798b18e75d51ee39f65b0b'`
Executing this git command manually:
```
Unknown option: -c
usage: git [--version] [--exec-path[=GIT_EXEC_PATH]] [--html-path]
[-p|--paginate|--no-pager] [--no-replace-objects]
[--bare] [--git-dir=GIT_DIR] [--work-tree=GIT_WORK_TREE]
[--help] COMMAND [ARGS]
```
Appears to have been introduced by rARC4600914