will force the perl confess / croak called from a C++ code to
print an error message and exit. There is a bug in some Strawberry
Perl instalations leading to an interpreter hang up and an exit
with a reasonable message is better than that.
Updated xs/Build.PL to understand BOOST_LIBRARY_PATH and
BOOST_INCLUDE_PATH environment variables. This way one may easily
switch between various boost builds.
Some minor tweeks were done to make Slic3r compile with
Visual Studio 2013.
