Issue #103: allow Infinity and -Infinity to be parsed.
diff --git a/configure.ac b/configure.ac
index 96e2466..20ad715 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,6 +29,7 @@
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
 AC_CHECK_FUNCS(strcasecmp strdup strerror snprintf vsnprintf vasprintf open vsyslog strncasecmp setlocale)
+AC_CHECK_DECLS([INFINITY], [], [], [[#include <math.h>]])
 AC_CHECK_DECLS([nan], [], [], [[#include <math.h>]])
 AC_CHECK_DECLS([isnan], [], [], [[#include <math.h>]])
 AC_CHECK_DECLS([isinf], [], [], [[#include <math.h>]])