[gimp] build/win: Reset tarball location on newer jhbuild versions.

[Michael Henning <mhenning src gnome org>]

commit a4bf1ff1cb57f97f0e588e2b9f40b31df1f3abd3
Author: Michael Henning <drawoc darkrefraction com>
Date:   Wed Jul 30 10:33:09 2014 -0400

    build/win: Reset tarball location on newer jhbuild versions.

 build/windows/jhbuild/build.jhbuildrc |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/build/windows/jhbuild/build.jhbuildrc b/build/windows/jhbuild/build.jhbuildrc
index 2d3fef6..2aaa659 100644
--- a/build/windows/jhbuild/build.jhbuildrc
+++ b/build/windows/jhbuild/build.jhbuildrc
@@ -30,6 +30,7 @@ else:
 # prefix:       target path to install the compiled binaries
 checkoutroot = os.environ['PWD']+'/checkout/'
 prefix = os.environ['PWD'] + '/targets/' + module + flavour_ext + '/'
+tarballdir = None
 
 os.environ['prefix'] = prefix