detect if command not available (usefull for windows users)

lib/capybara_webkit_builder.rb

@@ -29,12 +29,23 @@ module CapybaraWebkitBuilder
     end
   end
 
+  def sh(command)
+    system(command)
+    success = $?.exitstatus == 0
+    if $?.exitstatus == 127
+      puts "Command '#{command}' not available"  
+    elsif !success
+      puts "Command '#{command}' failed"
+    end
+    success
+  end
+
   def makefile
-    system("#{qmake_bin} -spec #{spec}")
+    sh("#{qmake_bin} -spec #{spec}")
   end
 
   def qmake
-    system("#{make_bin} qmake")
+    sh("#{make_bin} qmake")
   end
 
   def path_to_binary
@@ -47,7 +58,7 @@ module CapybaraWebkitBuilder
   end
 
   def build
-    system(make_bin) or return false
+    sh(make_bin) or return false
 
     FileUtils.mkdir("bin") unless File.directory?("bin")
     FileUtils.cp(path_to_binary, "bin", :preserve => true)