fix: Solve an issue where rewrites due to APPEND_SLASH_FOR_POSSIBLE_DIRECTORY would cause duplication of the query string

[4141done]

What

As reported here #205 when

• APPEND_SLASH_FOR_POSSIBLE_DIRECTORY=true
• ALLOW_DIRECTORY_LIST=false
• PROVIDE_INDEX_PAGE=true
  Are set, requests containing query strings without a trailing slash were being duplicated (foo?a=b were becoming foo?a=b?a=b).

Cause

The rewrite directive will automatically append the query string unless a final trailing ? is supplied. This was causing the duplication

Fix

Added an explanatory comment and a trailing ? to the rewrite rule to prevent automatic appending of the query string as we already do it in the argument to the rewrite rule.

I chose to do this rather than depending on the default behavior of rewrite since the rule as it is expressed is more explicit. The trailing ? is mysterious and so a comment was included to clarify.