Add . 'default' test first before searching paths, to determine if the

lua.h, liblua5.1, liblua-5.1 or liblua can be resolved.  This avoids
adding strange paths on fedora/redhat, and choosing the wrong /lib[64]
flavor.

Also ensure -lm is always added to the actual linked libraries, avoiding
a LoadModule failure on fedora/redhat.  Still should first try to search 
for pkg-config lua settings, but note this would break fedora until that
build hackery is corrected, c.f. the bug
https://bugzilla.redhat.com/show_bug.cgi?id=499238



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@772864 13f79535-47bb-0310-9956-ffa450edef68