rake doc:upload: check for wrong/incomplete rev

Rakefile

@@ -67,7 +67,16 @@ namespace :doc do
       Dir.glob("doc/images/*").each do |file|
         FileUtils.cp file, 'doc/gh-pages/images'
       end
-      rev = `git rev-parse --verify HEAD`
+      curRev = `git rev-parse --verify HEAD`.chomp()
+      expRev = IO.read('doc/html-revision').chomp()
+      if curRev != expRev
+        raise ("The HTML rev: #{expRev},\n" +
+               "current  rev: #{curRev}!\n")
+      end
+      if !system "git diff-index --quiet HEAD"
+        system "git status --untracked-files=no"
+        raise "You have uncommitted changes!"
+      end
       Dir.chdir 'doc/gh-pages' do
         sh "git commit -a -m 'Automatic documentation update.\n\n" +
           "From #{rev.chomp()}'"