[frogr] Don't allow running generate-SOURCES while in a JHBuild session

[Mario Sanchez Prada <msanchez src gnome org>]

commit 2333e40852f46df5419f26fbadb27cfe2aaef1df
Author: Mario Sanchez Prada <msanchez gnome org>
Date:   Thu Dec 20 12:18:28 2012 +0100

    Don't allow running generate-SOURCES while in a JHBuild session

 osx/generate-SOURCES |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/osx/generate-SOURCES b/osx/generate-SOURCES
index ef2f22e..682ce1c 100755
--- a/osx/generate-SOURCES
+++ b/osx/generate-SOURCES
@@ -5,6 +5,11 @@
 # used to build the DMG file to distribute the app for Mac OS X
 #
 
+if [ "x$JHBUILD_PREFIX" != "x" ]; then
+    echo "Can't run this script inside a JHBuild session. Please exit first"
+    exit 1;
+fi
+
 export JHB="frogr"
 
 jhb_cmd="$HOME/.local/bin/jhbuild"