Add a note about configure.ac being called configure.in

Sponsored by:	Absolight


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45660 c2e8774f-c49f-e111-b436-862b2bbc8956
Document USES=pear.

Sponsored by:	Absolight


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45661 c2e8774f-c49f-e111-b436-862b2bbc8956