fix installation issues with prerelease base gem versions

Author: denofevil

ext/mkrf_conf.rb

@@ -2,22 +2,32 @@
 unless jruby
   require 'rubygems'
   require 'rubygems/command.rb'
+  require 'rubygems/dependency.rb'
   require 'rubygems/dependency_installer.rb'
 
   begin
     Gem::Command.build_args = ARGV
     rescue NoMethodError
   end
 
-  inst = Gem::DependencyInstaller.new(:prerelease => true)
+  if RUBY_VERSION < "1.9"
+    dep = Gem::Dependency.new("ruby-debug-base", '>=0.10.4')
+  else
+    dep = Gem::Dependency.new("ruby-debug-base19x", '>=0.11.24')
+  end
+
+  inst = Gem::DependencyInstaller.new
   begin
-    if RUBY_VERSION < "1.9"
-      inst.install "ruby-debug-base", '>=0.10.4'
-    else
-      inst.install "ruby-debug-base19x", '>=0.11.24'
-    end
-    rescue
+    inst.install dep
+  rescue
+    inst = Gem::DependencyInstaller.new(:prerelease => true)
+    begin
+      inst.install dep
+    rescue Exception => e
+      puts e
+      puts e.backtrace.join "\n  "
       exit(1)
+    end
   end
 end