Make mod_include check for BYTE_COUNT_THRESHOLD on a per-bucket basis

Make mod_include check for BYTE_COUNT_THRESHOLD on a per-bucket basis
rather than on a per-character basis.  A significant amount of time
was spent checking the limit.  A better place to check for the threshold
is when we read the bucket in not as we read each character in the bucket.

If a bucket manages to be 200MB, it is not this code's problem as it
is a mere filter.

I ran this with the mod_include stuff in httpd-test and it looks good
from here.

Submitted by:	Brian Pane <bpane@pacbell.net>
Reviewed by:	Justin Erenkrantz, Ryan Bloom, Greg Stein, Cliff Woolley,
		Paul Reder, etc, etc, etc...

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90869 13f79535-47bb-0310-9956-ffa450edef68