Follow up to r1840149: core input filter pending data.

Follow up to r1840149: core input filter pending data.

Since r1840149 ap_core_input_filter() can't use use f->[priv->]bb directly, so
ap_filter_input_pending() stopped accounting for its pending data.

But ap_core_input_filter() can't (and doesn't need to) setaside its socket
bucket, so ap_filter_setaside_brigade() is not an option. This commit adds
ap_filter_adopt_brigade() which simply moves the given buckets (brigade) into
f->priv->bb, and since this is not something to be done blindly (the buckets
need to have c->pool/bucket_alloc lifetime, which is the case in the core
filter) the function is not AP_DECLAREd/exported thus can be used in core only.

With ap_filter_adopt_brigade() and ap_filter_reinstate_brigade(), the core
input is now ap_filter_input_pending() friendly.

Also, ap_filter_recycle() is no more part of the API (AP_DECLARE removed too),
there really is no point to call it outside core code. MAJOR bumped once again
because of this.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1840265 13f79535-47bb-0310-9956-ffa450edef68