Why:
* Want to add feature to stowrc parsing.
* Missing regression test for conflicting cli and stowrc options.
This change addresses the need by:
* Add missing regression tests to rc_options.t
* Two types of tests for the two types of options possible.
* For scalar options such as --target, cli arguments should overwrite
stowrc arguments.
* For options that result in a list, such as --ignore, the arguments
from cli and stowrc files should be merged.
ebc895a540