mod_perl.h is needed by perl module Apache::Table, which is used by RT (<a href="http://www.bestpractical.com/rt">http://www.bestpractical.com/rt</a>).
Fixed by APACHE_HEADER_INSTALL=1
*** Bug 917 has been marked as a duplicate of this bug. ***
ab@ asked to take over the package.
While I'm definitely not the best maintainer, hope that in three we'll cope with it.
fixed in 1.3.28-alt1
someone close me :-)