Problem:    "make clean" in top dir does not cleanup indent test output.
Solution:   Clean the indent test output.  Do not rely on the vim executable
            for that. (closes #4307)

Problem:    Indent script tests pick up installed scripts.
Solution:   Use current runtime indent scripts.

Problem:    When executing indent tests user preferences interfere.
Solution:   Add "--clean".

Problem:    No tests for indent files.
Solution:   Add a mechanism for running indent file tests.  Add a first test
            for Vim indenting.