ensure the merged header IS_STRING
ensure the merged header IS_STRING

git-svn-id: c060a288f18ad2989b40e1d0bb96bb4b9e86b00e@303221 c90b9560-bf6c-de11-be94-00142212c4b1

svn2github/pecl-http-v2,svn2github/pecl-http-v2,svn2github/pecl-http-v2