Fix include logic where include path is subdirectory of excluded path.

[shendy-a8c]

Fixes #172.

Changes in this PR:

• Fix containsMatchingChildren(), so $root_relative_path doesn't have trailing slash. [#]. This is because $include and $exclude are trailing-slash-trimmed, so if $root_relative_path isn't, this clause won't be true as expected.
• When the file iterator gets to the included folder, which is a subfolder of an excluded folder, it will get here, so I created a new if block to handle that case.
• Unit test for this case: including a folder inside an excluded folder.

[swissspidy]

Thanks a lot for this PR!

[shendy-a8c]

@swissspidy I'm not rushing but just want to make sure if there is any action item on my side.