remove 'ost' directory from sys.path

since the ost startup script lives in the same directory as the
top-level ost modules (python{version}/site-packages/ost), the
directory got automatically added to sys.path. That's bad for
several reasons I don't want to go in right now (see discussion
on the mailing list). Instead of passing the script as a script
name to execute, we now use execfile with the startup script.
This circumvents addition of the directory to the path and
makes Gabriel smile again.

scripts/ost.in

@@ -31,6 +31,6 @@ BIN_DIR=`dirname "$SCRIPT_NAME"`
 
 source "$BIN_DIR/../@LIBEXEC_PATH@/ost_config"
 
-$pyexec $interactive "$DNG_ROOT/@LIBDIR@/python@PYTHON_VERSION@/site-packages/ost/ost_startup.py" $opts
+$pyexec $interactive -c "execfile('$DNG_ROOT/@LIBDIR@/python@PYTHON_VERSION@/site-packages/ost/ost_startup.py')" $opts
 RC=$?
 exit $RC