Our two build systems can generate almost entirely a modulemap file laying out
one module per library. Due to some non-modular implementation in ROOT's core we
still need to treat some header files specially.

This patch appends modular header files to the modulemap while skipping the
predefined ones. Configure-make relates all headers that are installed in
$ROOTSYS/include to their library whereas relates only headers which are part of
library's dictionary.

Decouple redirection state from MetaProcessor and MaybeRedirectOutputRAII.
Only suspend redirection when writing to the prompt.
Allow user to redirect to files named 1, 2, &1, &2.
Allow stderr and stdout to be redirected to one another.
Don't create _IO_2_1_stdout_ file.

This allows the test to pass on VStudio 2015 and seems like a good thing
to test on other platforms.

Optimize InputValidator to avoid unnecessary copy when retrieving the input directly before a reset, and to release memory when reset.

Don't reallocate MetaLexer on the heap for every line. Its a waste of time for 24 bytes that will be needed for every line anyway. Remove bufferEnd field as it was entirely unused.