Improve the english a bit and make the previous error message cleaner

src/IDF/templates/idf/source/invalid_revision.html

@@ -2,10 +2,10 @@
 {block docclass}yui-t2{assign $inError=true}{/block}
 {block body}
 
-<p>{blocktrans}The revision <b>{$commit}</b> is not valid or does not exist
+<p>{blocktrans}The branch or revision <b>{$commit}</b> is not valid or does not exist
 in this repository.{/blocktrans}</p>
 
-<p>{blocktrans}List of available branch are listed below :{/blocktrans}</p>
+<p>{blocktrans}The following list shows all available branches:{/blocktrans}</p>
 <ul>
 {foreach $branches as $branch => $path}
 {aurl 'url', 'IDF_Views_Source::treeBase', array($project.shortname, $branch)}