Unbreak MOE by adding a .gitignore to extensions (suppressing build/ folders under it) and narrowing the exclusion of bduild folders in the root to just at the root.  This lets /lib/build exist and be used, including by MOE.
diff --git a/.gitignore b/.gitignore
index f4ceeb7..2507017 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
-build/
+/build/
 target/
 bin/
 .project