Fix for issue #3334: build not finding YAJL

When searching for YAJL during ./configure, pkg-config is checked first,
and then a list of directories is searched if pkg-config bears no fruit.
The previous version of yajl.m4 was looping over YAJL_POSSIBLE_LIB_NAMES
instead of YAJL_POSSIBLE_PATHS and passing the lib name to the
CHECK_FOR_YAJL_AT() function instead of the path. The would lead to YAJL
never being found if pkg-config could not find it.

Author: RooHTaylor

build/yajl.m4

@@ -62,7 +62,7 @@ else
                 YAJL_DISPLAY="${YAJL_LDADD}, ${YAJL_CFLAGS}"
             else
                 # If pkg-config did not find anything useful, go over file lookup.
-                for x in ${YAJL_POSSIBLE_LIB_NAMES}; do
+                for x in ${YAJL_POSSIBLE_PATHS}; do
                     CHECK_FOR_YAJL_AT(${x})
                     if test -n "${YAJL_VERSION}"; then
                         break