tools should not override existing path order

[dmoody256]

This is a potential solution to #3276.

This sets all tools to not delete existing paths, maintaining the original environment.

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated master/src/CHANGES.txt directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

[coveralls]

Coverage decreased (-0.0009%) to 79.984% when pulling 41280fe on dmoody256:tools_path_appending_issue into e44c771 on SCons:master.

[bdbaddog]

Is there anywhere left in scons where delete_existing is defaulted?
Perhaps it makes more sense to change the default?
I can't imagine that the "normal" usage would want to move it to the end of a given path?

[dmoody256]

Is there anywhere left in scons where delete_existing is defaulted?
Perhaps it makes more sense to change the default?
I can't imagine that the "normal" usage would want to move it to the end of a given path?

I made another to test that out PR #3281

[dmoody256]

I think I will close this PR in favor of changing the default and updating the test in #3281?

[bdbaddog]

O.k. Closing.