For ruby 1.9.3, prefer a version of ruby-debug-base19x that doesn't depend on linecache19 nor columnize gems

Author: francoisjacques

ext/mkrf_conf.rb

@@ -19,6 +19,8 @@ def already_installed(dep)
 
   if RUBY_VERSION < "1.9"
     dep = Gem::Dependency.new("ruby-debug-base", '>=0.10.4')
+  elsif RUBY_VERSION >= '1.9.3'
+    dep = Gem::Dependency.new("ruby-debug-base19x", '>=0.11.30.pre15')
   elsif RUBY_VERSION < '2.0'
     dep = Gem::Dependency.new("ruby-debug-base19x", '>=0.11.24')
   else    
@@ -27,11 +29,11 @@ def already_installed(dep)
 
   begin
     puts "Installing base gem"
-    inst = Gem::DependencyInstaller.new    
+    inst = Gem::DependencyInstaller.new :prerelease => dep.prerelease?
     inst.install dep
   rescue
-    inst = Gem::DependencyInstaller.new(:prerelease => true)
     begin
+      inst = Gem::DependencyInstaller.new(:prerelease => true)
       inst.install dep
     rescue Exception => e
       puts e