Allow Spack Environments with '-h' in the name (#15429)

If a user invoked "spack env activate example-henv", Spack would
mistakenly interpret the "-h" from "example-henv" as the "-h" option.
This commit allows users to create and activate environments with
"-h" in the name.

This issue existed for bash shell support as well as csh support, and
this commit addresses both, along with some other unrelated csh
support issues.