When translating, Check that the extensions the user asked for are pr…

…esent.

Before --withext-* (or --allexts) would silently be ignored if external
extension source code was missing.

targethippy.py

@@ -12,9 +12,18 @@ def target(driver, args):
     parser = to_optparse(config, parserkwargs={'usage': SUPPRESS_USAGE })
     parser.parse_args(args)
 
+
+    from hippy.hippyoption import (
+        OPTIONAL_EXTS, is_optional_extension_enabled, HippyOptionError)
+
     from hippy.hippyoption import set_options
     set_options(config)
 
+    for ext in OPTIONAL_EXTS:
+        asked = getattr(config.optexts, ext)
+        if asked and not is_optional_extension_enabled(ext):
+            raise HippyOptionError("%s extension sources are missing!" % ext)
+
     from hippy.main import entry_point
     return entry_point, None