Install sqlalchemy-migrate from master if requested

Added possibility to install sqlalchemy-migrate from master instead of
pypi packages.

Change-Id: I8af92cbb03609799442b05db9772e3c82b76725b
diff --git a/lib/stackforge b/lib/stackforge
index b744318..2d80dad 100644
--- a/lib/stackforge
+++ b/lib/stackforge
@@ -29,6 +29,7 @@
 # --------
 WSME_DIR=$DEST/wsme
 PECAN_DIR=$DEST/pecan
+SQLALCHEMY_MIGRATE_DIR=$DEST/sqlalchemy-migrate
 
 # Entry Points
 # ------------
@@ -40,6 +41,9 @@
 
     git_clone $PECAN_REPO $PECAN_DIR $PECAN_BRANCH
     setup_package $PECAN_DIR
+
+    git_clone $SQLALCHEMY_MIGRATE_REPO $SQLALCHEMY_MIGRATE_DIR $SQLALCHEMY_MIGRATE_BRANCH
+    setup_package $SQLALCHEMY_MIGRATE_DIR
 }
 
 # Restore xtrace