As promised, reduce this logic by net 9 code lines, shifting the burden

As promised, reduce this logic by net 9 code lines, shifting the burden
of killing trailing whitespace to the purpose-agnostic read logic.

Whitespace before or after an obs-fold, and before or after a field value
have no semantic purpose at all. Because we are building a buffer for all
folded values, reducing the size of the newly allocated buffer is always
to our advantage.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1755233 13f79535-47bb-0310-9956-ffa450edef68