mesa: set version string to 7.7.1

Also set the correct release date.
(cherry picked from commit 663642b435af2f8ab4b16360783eb367f42486c3)
diff --git a/docs/relnotes-7.7.1.html b/docs/relnotes-7.7.1.html
index 46f4cac..699627d 100644
--- a/docs/relnotes-7.7.1.html
+++ b/docs/relnotes-7.7.1.html
@@ -8,7 +8,7 @@
 
 <body bgcolor="#eeeeee">
 
-<H1>Mesa 7.7.1 Release Notes / March 26, 2010</H1>
+<H1>Mesa 7.7.1 Release Notes / March 28, 2010</H1>
 
 <p>
 Mesa 7.7.1 is a bug-fix release.