Problem: inttypes.h not available for MSVC, to provide PRId64

Solution: define PRId64 conditionally for Windows
Merge pull request #763 from hintjens/master

Problem: inttypes.h not available for MSVC, to provide PRId64
Define PRId64 as string literal.
Match s_client_execute prototype to implementation.
Fix 'forcing to bool' msvc warning.
Merge pull request #764 from evoskuil/master

Build breaks in msvc 2010/12/13.