Fix double-prefixed path in outdate-bundled-gems.rb (ruby#16531)

When building with a relative srcdir (e.g., ../configure from a build
directory), default_gem? was called with an already-prefixed path on
line 149. Since default_gem? internally calls prefixed() again, this
resulted in a double prefix (e.g., ../../.bundle/... instead of
../.bundle/...), causing an ENOENT error.

Also fix line 156 to use curdir.default_gem? instead of srcdir, since
the spec comes from curdir.glob and should be resolved against curdir.

Author: k0kubun

tool/outdate-bundled-gems.rb

@@ -146,14 +146,14 @@ def each_directory
 
 srcdir.glob(".bundle/specifications/*.gemspec") do |spec|
   unless srcdir.directory?(".bundle/gems/#{File.basename(spec, '.gemspec')}/")
-    next if srcdir.default_gem?(srcdir.prefixed(spec))
+    next if srcdir.default_gem?(spec)
     srcdir.unlink(spec)
   end
 end
 
 curdir.glob(".bundle/specifications/*.gemspec") do |spec|
   unless srcdir.directory?(".bundle/gems/#{File.basename(spec, '.gemspec')}")
-    next if srcdir.default_gem?(curdir.prefixed(spec))
+    next if curdir.default_gem?(spec)
     curdir.unlink(spec)
   end
 end