Build Revision Info Added

Travis now overwrites RevisionIdent.h to place a commit reference into the Build Info of the AboutDialog
I also added .opensdf to .gitignore.

src/AboutDialog.cpp

@@ -549,6 +549,10 @@ void AboutDialog::PopulateInformationPage( ShuttleGui & S )
    // Current date
    AddBuildinfoRow(&informationStr, _("Program build date: "), __TDATE__);
 
+   AddBuildinfoRow(&informationStr, _("Commit Id:"),
+#include "RevisionIdent.h"
+);
+
 #ifdef __WXDEBUG__
    AddBuildinfoRow(&informationStr, _("Build type:"), _("Debug build"));
 #else

src/RevisionIdent.h

@@ -0,0 +1,28 @@
+/**********************************************************************
+
+   Audacity: A Digital Audio Editor
+   Audacity(R) is copyright (c) 1999-2015 Audacity Team.
+   License: GPL v2.  See License.txt.
+
+   RevisionIdent.h
+
+
+********************************************************************//*!
+
+\file RevisionIdent.h
+
+  This entire file will be replaced by the revision identifier string 
+  based on the branch SHA when the automated build system builds
+  Audacity.  That striing will look something like:
+
+  "<a href=\"https://github.com/audacity/audacity/commit/
+  7f2e83995596367aeed69f3086ac9fd2039795a3\">7f2e839</a> of 
+  Thu Apr 9 20:03:11 2015 +0100"
+
+*//********************************************************************/
+
+// The string below is what you get if 
+// the build system does not replace this file.
+
+wxT("No revision identifier was provided")
+