Move definition of GEM_EXTSDIR and PRINT_PLIST_AWK definition block to
appropriate place.  Noted by obache@.
The CPPFunction typedef (among others) have been deprecated in favour of
specific prototyped typedefs since readline 4.2.
They've been working since because compatibility typedefs have been
until they were removed in readline 6.3.

Hint found here: https://bugs.gentoo.org/show_bug.cgi?id=504208
Revert to treetop-1.4.15 since ruby-rail require prior to 1.5.

Thanks to hiramatsu@.
Update of textproc/ruby-treetop to 1.5.1 was reverted.