Differentiate nitra results through exit codes

This will allow determining whether there were only test failures or if
running the build actually failed itself.

README.md

@@ -4,7 +4,7 @@ Nitra is a multi-process, optionally multi-server rspec and cucumber runner that
 ## Philosophy
 * Nitra attempts to do the simplest thing possible
 * Nitra (ab)uses unix primitives where possible
-* Nitra doesn't do thing that unix alnext_file does better (eg. rsync)
+* Nitra doesn't do things that unix already does better (eg. rsync)
 * IPC is accomplished via pipes and select
 * Forking is used heavily for several reasons
 * Running nitra locally should be easy

bin/nitra

@@ -8,5 +8,20 @@ Nitra::CommandLine.new(configuration, ARGV)
 if configuration.slave_mode
   Nitra::Slave::Server.new.run
 else
-  exit Nitra::Master.new(configuration, ARGV).run ? 0 : 1
+  result = Nitra::Master.new(configuration, ARGV).run
+
+  case result
+  when Nitra::Master::ABORTED
+    exit 1
+  when Nitra::Master::TEST_FAILURES
+    exit 2
+  when Nitra::Master::FAILURE
+    exit 3
+  when Nitra::Master::UNPROCESSED_FILES
+    exit 4
+  when Nitra::Master::SUCCESS
+    exit 0
+  else
+    exit 127
+  end
 end

lib/nitra/master.rb

@@ -1,6 +1,12 @@
 class Nitra::Master
   attr_reader :configuration, :files_by_framework
 
+  ABORTED           = :aborted
+  FAILURE           = :failure
+  SUCCESS           = :success
+  TEST_FAILURES     = :test_failures
+  UNPROCESSED_FILES = :unprocessed_files
+
   def initialize(configuration, files = nil)
     @configuration = configuration
     if configuration.frameworks.any?
@@ -43,7 +49,17 @@ def run
     formatter.finish
     burndown.finish configuration.burndown_report if configuration.burndown_report
 
-    !$aborted && progress.files_completed == progress.file_count && progress.failure_count.zero? && !progress.failure
+    if $aborted
+      ABORTED
+    elsif progress.files_completed != progress.file_count
+      UNPROCESSED_FILES
+    elsif progress.failure_count.positive?
+      TEST_FAILURES
+    elsif progress.failure
+      FAILURE
+    else
+      SUCCESS
+    end
   end
 
 protected