A user had `grep` aliased to `grep -n`, which was causing `csh` setup to
fail due to number prefixes in `SPACK_ROOT`.
- [x] Prefix invocations of `grep` and `sed` (which are not builtin) with `\`
to avoid any aliases.
- [x] Avoid using `dirname` altogether -- use csh's `:h` modifier (which does
the same thing) instead.
Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>
20ddb85020