fix PROGSUFFIX handling - close #29

build_tests/simple/progsuffix2.rb

@@ -0,0 +1,4 @@
+Rscons::Environment.new do |env|
+  env["MYSUFFIX"] = ".out"
+  env.Program("simple${MYSUFFIX}", Dir["*.c"])
+end

build_tests/simple/progsuffix3.rb

@@ -0,0 +1,3 @@
+Rscons::Environment.new do |env|
+  env.Program("simple", Dir["*.c"], "PROGSUFFIX" => ".xyz")
+end