Use raw-string syntax for Python string containing Windows pathname.

Consider this pathname for llsdserialize_test.cpp:
C:\nats\indra\llcommon\tests\llsdserialize_test.cpp
Embed that in a Python string literal:
'C:\nats\indra\llcommon\tests\llsdserialize_test.cpp'
and you get a string containing:
C:
ats\indra\llcommon	ests\llsdserialize_test.cpp
where the \n became a newline and the \t became a tab character.
Hopefully Python raw-string syntax r'C:\etc\etc' works better.