Added *.d files to .gitignore.  Those are dependency files generated by gcc -MD and such.

Review URL: http://codereview.chromium.org/618012
diff --git a/.gitignore b/.gitignore
index a138169..ea8ea0d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,7 +5,7 @@
 #
 
 # Standard ignores
-*.[ao]
+*.[aod]
 *.la
 *.lo
 *.pyc