Perform PATH home directory expansion.

Expands ~/ components inside PATH, which is shell agnostic.

This is what I intended in my original proposal for home directory expansion, as this doesn't involve rewriting the command and is completely shell agnostic.

$SHELL -c 'command' will already perform home expansion on the *command* (if supported by the shell). Performing ~ expansion in the command as well however doesn't hurt when the command isn't run through the shell -c flag.