While this uglifies the code, it removes a dependency on newer
boost 1.64+ which ships boost::process. This helps on systems
where LO is linked against system boost and an older version
of boost is used.

Additionally, and this is the main motivation, this makes it
easier to backport these changes to 5.2, where the bundled boost
is also only at 1.60.

To keep the required changes at a minimum, the osl_* API for
reading from/writing to the stdout/stdin of the helper process,
we buffer the responses on a line-by-line basis. Note that one
cannot simply reuse osl_readLine on the non-seekable oslFileHandle.
Instead, we have to roll our own simplistic readLine implementation...

Change-Id: I1197e38cb2416e926d8ba985accd6c10d78bcc52
Reviewed-on: https://gerrit.libreoffice.org/48490Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>