libs/mpl/preprocessed need README on purpose and howto

[cppljevans@…]

After application of recent patch file:

​https://svn.boost.org/trac/boost/attachment/ticket

/3044/iter_fold_if.patch

an attempt to run the test resulted in an error msg:

gcc.compile.c++ ../../../bin.v2/libs/mpl/test/iter_fold_if.test

/gcc-4.2/debug/iter_fold_if.o

In file included from iter_fold_if.cpp:14: ../../../boost/mpl/iter_fold_if.hpp:86: error: wrong number of

template arguments (5, should be 6)

../../../boost/mpl/aux_/preprocessed/gcc/iter_fold_if_impl.hpp:96:

error: provided for 'template<class Iterator, class State, class ForwardOp, class ForwardPredicate, class BackwardOp, class BackwardPredicate> struct boost::mpl::aux::iter_fold_if_impl'

This message indicates need to regenerate the preprocessed files from the programs in /mpl/lib/preprocessed; however, there's no README file in that directory providing instructions on how to do that.

It would be very helpful if one were provided.

[Steven Watanabe]

I tested using

bjam gcc define=BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS

AFAICT, the script that does the regeneration is preprocess.py, which does have a usage message.