Just cast the size() return value to long int, which of course can cause
breakage when the size_type (is that always the same as size_t?) is larger
than long int. For 64-bit Windows code size_t is 64 bits but long is 32
bits. I couldn't think of any simple totally correct solution that would work
also on compilers without <stdint.h> and <inttypes.h> (MSVC2008), or without
the z format specifier (all MSVC versions?).

(Our SAL_PRI_SIZET is not available to a 3rd-party library like
libcmis. Should libcmis grow corresponding configury to find out that?)

Why does a C++ library like libcmis use C-style printf formats anyway? ;)

Change-Id: I093655577bc1a50c137c79b648058f0823cc66c1