Allow dev FFI loading with preload environment

ober

a861227afb4a6e343a358b5bfec1700989ee479d

diff --git a/jerboa-src/src/jsh/ffi.ss b/jerboa-src/src/jsh/ffi.ss
index 4abbadf..59de073 100644
--- a/jerboa-src/src/jsh/ffi.ss
+++ b/jerboa-src/src/jsh/ffi.ss
@@ -125,8 +125,9 @@
        (error 'jsh-load-ffi-shared-objects!
               "dynamic FFI loading is unavailable in a privileged process")]
       [else
-       (native-loader-require-clean-environment!
-         'jsh-load-ffi-shared-objects!)
+       (unless (native-loader-development-enabled? "JSH_FFI_DEV_NATIVE")
+         (native-loader-require-clean-environment!
+           'jsh-load-ffi-shared-objects!))
        (let ([path (jsh-configured-library)])
          (unless (jsh-load-candidate path)
            (error 'jsh-load-ffi-shared-objects!