Fixes https://github.com/json-c/json-c/issues/909
When ssize_t is defined as a macro, typically through a package's config.h file,
the installed json*.h files must not attempt to define ssize_t via typedef.
As part of this create a public json_config.h with a custom define to
decide whether to include inttypes.h to avoid conflicting with other
projects config.h header.
json_object_get_int64. Binary compatibility preserved.
Eric Haszlakiewicz, EHASZLA at transunion com
Rui Miguel Silva Seabra, rms at 1407 dot org
git-svn-id: http://svn.metaparadigm.com/svn/json-c/trunk@56 327403b1-1117-474d-bef2-5cb71233fd97