Ignore "build" dir for out-of-source build testing.

--HG--
branch : HEAD
diff --git a/.hgignore b/.hgignore
index 453464a..ea54d5c 100644
--- a/.hgignore
+++ b/.hgignore
@@ -9,6 +9,7 @@
 \.pc$
 ^aclocal.m4$
 ^autom4te\.cache/
+^build
 ^config\.(h|status|log|h\.in)$
 ^configure$
 ^libtool$