add native fake sendmail instead of bash script

This is an attempt at fixing a frequent testsuite hang on Windows.

t9001 sporadically hangs on Windows when the full testsuite is run.
The exact reason is unclear since it does not happen when the test is run
individually. We assume that for some reason when forking another sh
from within the send-email perl script the child tree becomes to deep and
that breaks somehow the pipe connection between parent and child because
of some speciality in the msys posix emaulation layer. The data flow hangs
and either child or parent waits forever. We work around this by compiling
our own c code that is not linked to msys.

In our tests we did not experience any hangs, so this hopefully fixes the
problem.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>