Bit friendlier error message on invalid config

Closes #20

[ytti@ytti.fi ~/tmp/oxidized]% oxidized
Error loading config: (<unknown>): mapping values are not s context at line 15 column 7
[ytti@ytti.fi ~/tmp/oxidized]%

bin/oxidized

@@ -1,5 +1,6 @@
 #!/usr/bin/env ruby
 
+
 # FIX ME, killing oxidized needs -9
 trap("INT") { exit } # sinatra will otherwise steal this from us
 

lib/oxidized/config.rb

@@ -1,6 +1,7 @@
 module Oxidized
   require 'asetus'
   class NoConfig < OxidizedError; end
+  class InvalidConfig < OxidizedError; end
   class Config
     Root      = File.join ENV['HOME'], '.config', 'oxidized'
     Crash     = File.join Root, 'crash'
@@ -39,8 +40,13 @@ class << self
     'juniper' => 'junos',
   }
 
-  CFGS.load       # load system+user configs, merge to Config.cfg
-  CFG = CFGS.cfg  # convenienence, instead of Config.cfg.password, CFG.password
+  begin
+    CFGS.load # load system+user configs, merge to Config.cfg
+  rescue => error
+    raise InvalidConfig, "Error loading config: #{error.message}"
+  ensure
+    CFG = CFGS.cfg  # convenienence, instead of Config.cfg.password, CFG.password
+  end
 
   Log.level = Logger::INFO unless CFG.debug
   raise NoConfig, 'edit ~/.config/oxidized/config' if CFGS.create