This removes the ability to override standard shell utilities using
environment variables. The standard names are invoked unconditionally and
can be overridden using the standard approach of adding replacements to the
PATH. Additionally environment variables like PREFIX and HOST are no longer
honored as defaults for the --prefix and --host options. These features are
removed because they've never been used and cause more trouble than they
are worth.
The tix collection option now defaults to the root directory to simplify
common invocations. The tix-build prefix also now defaults to the empty
prefix.
Support installing multiple packages at once with tix-install.
Tighten file and directory creation modes while here.
Add --generation for forward compatibility.
Silence tix-collection creation.
Fix uninitialized getline invocations.
Fix porttix-create buffer overflow.
